FlightGear support for queued commands

This enables queued commands to be processed once per main event loop.
At present this is done after subsystem updates.

src/Main/fg_commands.cxx

@@ -970,6 +970,10 @@ static struct {
 void
 fgInitCommands ()
 {
+  // set our property root as the implicit default root for the
+  // command managr
+  SGCommandMgr::instance()->setImplicitRoot(globals->get_props());
+    
   SG_LOG(SG_GENERAL, SG_BULK, "Initializing basic built-in commands:");
   for (int i = 0; built_ins[i].name != 0; i++) {
     SG_LOG(SG_GENERAL, SG_BULK, "  " << built_ins[i].name);

src/Main/fg_init.cxx

@@ -1194,6 +1194,9 @@ void fgStartNewReset()
     fgInitConfig(0, NULL, true);
     fgInitGeneral(); // all of this?
     
+    // set out new property root on the command manager
+    SGCommandMgr::instance()->setImplicitRoot(globals->get_props());
+    
     flightgear::Options::sharedInstance()->processOptions();
 
     // Rebuild the lists of allowed paths for cases where a path comes from an

src/Main/main.cxx

@@ -55,6 +55,7 @@ extern bool global_crashRptEnabled;
 #include <simgear/math/SGMath.hxx>
 #include <simgear/math/sg_random.h>
 #include <simgear/misc/strutils.hxx>
+#include <simgear/structure/commands.hxx>
 
 #include <Add-ons/AddonManager.hxx>
 #include <Main/locale.hxx>
@@ -122,6 +123,8 @@ static void fgMainLoop( void )
     // update all subsystems
     globals->get_subsystem_mgr()->update(sim_dt);
 
+    // flush commands waiting in the queue
+    SGCommandMgr::instance()->executedQueuedCommands();
     simgear::AtomicChangeListener::fireChangeListeners();
 }