prepare for subsystem_mgr.hxx no longer including props.hxx

subsystem_mgr.hxx will soon no longer include props.hxx since it
does not (need to) know about properties at all.

src/Environment/realwx_ctrl.hxx

@@ -24,7 +24,7 @@
 #define _REALWX_CTRL_HXX
 
 #include <simgear/structure/subsystem_mgr.hxx>
-
+#include <simgear/props/props.hxx>
 namespace Environment {
 class RealWxController : public SGSubsystem
 {

src/Instrumentation/dclgps.hxx

@@ -33,6 +33,7 @@
 #include <map>
 
 #include <simgear/structure/subsystem_mgr.hxx>
+#include <simgear/props/props.hxx>
 #include <Navaids/positioned.hxx>
 
 class SGTime;

src/Main/logger.hxx

@@ -11,6 +11,7 @@
 
 #include <simgear/compiler.h>
 #include <simgear/structure/subsystem_mgr.hxx>
+#include <simgear/props/props.hxx>
 
 /**
  * Log any property values to any number of CSV files.

src/Main/viewmgr.hxx

@@ -29,6 +29,7 @@
 
 #include <simgear/compiler.h>
 #include <simgear/structure/subsystem_mgr.hxx>
+#include <simgear/props/props.hxx>
 #include <simgear/math/SGMath.hxx>
 
 // forward decls

src/Sound/fg_fx.hxx

@@ -29,6 +29,7 @@
 #include <vector>
 
 #include <simgear/structure/subsystem_mgr.hxx>
+#include <simgear/props/props.hxx>
 #include <simgear/sound/sample_group.hxx>
 
 class SGXmlSound;

src/Sound/sample_queue.hxx

@@ -29,6 +29,7 @@
 #include <queue>
 
 #include <simgear/structure/subsystem_mgr.hxx>
+#include <simgear/props/props.hxx>
 #include <simgear/sound/sample_group.hxx>
 
 class SGSoundSample;

src/Time/TimeManager.hxx

@@ -22,6 +22,7 @@
 #define FG_TIME_TIMEMANAGER_HXX
 
 #include <simgear/structure/subsystem_mgr.hxx>
+#include <simgear/props/props.hxx>
 
 // forward decls
 class SGTime;