diff --git a/src/Aircraft/Makefile.am b/src/Aircraft/Makefile.am
index af6998277..18f90349e 100644
--- a/src/Aircraft/Makefile.am
+++ b/src/Aircraft/Makefile.am
@@ -2,4 +2,4 @@ noinst_LIBRARIES = libAircraft.a
 
 libAircraft_a_SOURCES = aircraft.cxx aircraft.hxx
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/Autopilot/Makefile.am b/src/Autopilot/Makefile.am
index 3d0623429..0102e4a4a 100644
--- a/src/Autopilot/Makefile.am
+++ b/src/Autopilot/Makefile.am
@@ -4,4 +4,4 @@ libAutopilot_a_SOURCES = \
 	auto_gui.cxx auto_gui.hxx \
 	newauto.cxx newauto.hxx
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/Cockpit/Makefile.am b/src/Cockpit/Makefile.am
index 69fd6c8a1..ac7a8b11d 100644
--- a/src/Cockpit/Makefile.am
+++ b/src/Cockpit/Makefile.am
@@ -13,4 +13,4 @@ libCockpit_a_SOURCES = \
 	sp_panel.cxx sp_panel.hxx \
 	steam.cxx steam.hxx
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/Controls/Makefile.am b/src/Controls/Makefile.am
index 8b63268eb..c05f6e90a 100644
--- a/src/Controls/Makefile.am
+++ b/src/Controls/Makefile.am
@@ -2,4 +2,4 @@ noinst_LIBRARIES = libControls.a
 
 libControls_a_SOURCES = controls.cxx controls.hxx
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/FDM/Balloon/Makefile.am b/src/FDM/Balloon/Makefile.am
index b06970098..2d4ac60c7 100644
--- a/src/FDM/Balloon/Makefile.am
+++ b/src/FDM/Balloon/Makefile.am
@@ -2,4 +2,4 @@ noinst_LIBRARIES = libBalloon.a
 
 libBalloon_a_SOURCES = BalloonSim.cpp BalloonSim.h
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/FDM/JSBSim/Makefile.am b/src/FDM/JSBSim/Makefile.am
index 5e89b59a3..a5203fca3 100644
--- a/src/FDM/JSBSim/Makefile.am
+++ b/src/FDM/JSBSim/Makefile.am
@@ -34,6 +34,6 @@ testJSBsim_SOURCES = JSBSim.cpp
 
 testJSBsim_LDADD = libJSBSim.a filtersjb/libfiltersjb.a
 
-INCLUDES += -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir)/src
 
 DEFS += -DFGFS
diff --git a/src/FDM/JSBSim/filtersjb/Makefile.am b/src/FDM/JSBSim/filtersjb/Makefile.am
index 8c5e09f1f..f64258101 100644
--- a/src/FDM/JSBSim/filtersjb/Makefile.am
+++ b/src/FDM/JSBSim/filtersjb/Makefile.am
@@ -12,6 +12,6 @@ libfiltersjb_a_SOURCES = \
 	FGSummer.cpp FGSummer.h \
 	FGSwitch.cpp FGSwitch.h
 
-INCLUDES += -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir)/src
 
 DEFS += -DFGFS
diff --git a/src/FDM/LaRCsim/Makefile.am b/src/FDM/LaRCsim/Makefile.am
index 8f5ba663e..d50daf402 100644
--- a/src/FDM/LaRCsim/Makefile.am
+++ b/src/FDM/LaRCsim/Makefile.am
@@ -31,4 +31,4 @@ libLaRCsim_a_SOURCES = \
 	$(AIRCRAFT_MODEL) \
 	ls_interface.c ls_interface.h
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/FDM/Makefile.am b/src/FDM/Makefile.am
index ff12202fe..d10e3ac81 100644
--- a/src/FDM/Makefile.am
+++ b/src/FDM/Makefile.am
@@ -19,4 +19,4 @@ engine_LDADD = libFlight.a
 
 pstest_SOURCES = ps-10520c.cxx
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/FDM/UIUCModel/Makefile.am b/src/FDM/UIUCModel/Makefile.am
index fd15bcefd..f5714293f 100644
--- a/src/FDM/UIUCModel/Makefile.am
+++ b/src/FDM/UIUCModel/Makefile.am
@@ -47,4 +47,4 @@ libUIUCModel_a_SOURCES = \
                         uiuc_warnings_errors.cpp uiuc_warnings_errors.h \
                         uiuc_wrapper.cpp uiuc_wrapper.h
 
-INCLUDES += -I$(top_builddir) 
+INCLUDES += -I$(top_srcdir) 
diff --git a/src/GUI/Makefile.am b/src/GUI/Makefile.am
index 5d4224413..927499f87 100644
--- a/src/GUI/Makefile.am
+++ b/src/GUI/Makefile.am
@@ -2,4 +2,4 @@ noinst_LIBRARIES = libGUI.a
 
 libGUI_a_SOURCES = gui.cxx gui.h
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/Include/config.h.in b/src/Include/config.h.in
index 2962401d4..13044e031 100644
--- a/src/Include/config.h.in
+++ b/src/Include/config.h.in
@@ -225,6 +225,9 @@
 /* Define if you have the m library (-lm).  */
 #undef HAVE_LIBM
 
+/* Define if you have the plibul library (-lplibul).  */
+#undef HAVE_LIBPLIBUL
+
 /* Define if you have the pthread library (-lpthread).  */
 #undef HAVE_LIBPTHREAD
 
diff --git a/src/Joystick/Makefile.am b/src/Joystick/Makefile.am
index a0d9801ea..ddbcecbf8 100644
--- a/src/Joystick/Makefile.am
+++ b/src/Joystick/Makefile.am
@@ -6,4 +6,4 @@ noinst_PROGRAMS = js_demo
 
 js_demo_SOURCES = js_demo.cxx
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/Main/Makefile.am b/src/Main/Makefile.am
index 13d700c4f..37bce676a 100644
--- a/src/Main/Makefile.am
+++ b/src/Main/Makefile.am
@@ -73,4 +73,4 @@ fgfs_LDADD = \
 	$(opengl_LIBS) \
 	$(audio_LIBS)
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/Navaids/Makefile.am b/src/Navaids/Makefile.am
index 1a020e7a3..a024c4113 100644
--- a/src/Navaids/Makefile.am
+++ b/src/Navaids/Makefile.am
@@ -10,4 +10,4 @@ libNavaids_a_SOURCES = \
 testnavs_SOURCES = testnavs.cxx
 testnavs_LDADD = libNavaids.a -lsgmath -lsgmisc -lsgdebug -lz
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/Network/Makefile.am b/src/Network/Makefile.am
index 305c3363a..7a049e9b3 100644
--- a/src/Network/Makefile.am
+++ b/src/Network/Makefile.am
@@ -10,4 +10,4 @@ libNetwork_a_SOURCES = \
 	rul.cxx rul.hxx \
 	joyclient.cxx joyclient.hxx
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/NetworkOLK/Makefile.am b/src/NetworkOLK/Makefile.am
index 9eb82a8c9..3e19336d5 100644
--- a/src/NetworkOLK/Makefile.am
+++ b/src/NetworkOLK/Makefile.am
@@ -4,4 +4,4 @@ libNetworkOLK_a_SOURCES = \
 	net_send.cxx net_hud.cxx network.cxx network.h fgd.h \
 	features.cxx features.hxx
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/Objects/Makefile.am b/src/Objects/Makefile.am
index 37e8db67e..57ccc7ae7 100644
--- a/src/Objects/Makefile.am
+++ b/src/Objects/Makefile.am
@@ -6,4 +6,4 @@ libObjects_a_SOURCES = \
 	obj.cxx obj.hxx \
 	texload.c texload.h colours.h
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/Scenery/Makefile.am b/src/Scenery/Makefile.am
index 978e30fd1..2476df614 100644
--- a/src/Scenery/Makefile.am
+++ b/src/Scenery/Makefile.am
@@ -7,4 +7,4 @@ libScenery_a_SOURCES = \
 	tileentry.cxx tileentry.hxx \
 	tilemgr.cxx tilemgr.hxx
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/Time/Makefile.am b/src/Time/Makefile.am
index 0ee9bf459..73ab68e0f 100644
--- a/src/Time/Makefile.am
+++ b/src/Time/Makefile.am
@@ -13,4 +13,4 @@ libTime_a_SOURCES = \
 	# lowleveltime.cxx lowleveltime.h \
 	# timezone.cxx timezone.h
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/Weather/Makefile.am b/src/Weather/Makefile.am
index cb4ba0620..b4dc076e5 100644
--- a/src/Weather/Makefile.am
+++ b/src/Weather/Makefile.am
@@ -6,4 +6,4 @@ noinst_LIBRARIES = libWeather.a
 
 libWeather_a_SOURCES = weather.cxx weather.hxx
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/WeatherCM/Makefile.am b/src/WeatherCM/Makefile.am
index b5a0b5048..a3b1e7bc2 100644
--- a/src/WeatherCM/Makefile.am
+++ b/src/WeatherCM/Makefile.am
@@ -18,4 +18,4 @@ libWeatherCM_a_SOURCES = \
 	FGWeatherVectorWrap.h \
 	FGWindItem.cpp FGWindItem.h
 
-INCLUDES += -I$(top_builddir) -I$(top_builddir)/src
+INCLUDES += -I$(top_srcdir) -I$(top_srcdir)/src