remove util.cxx workaround for listener-call-at-exit-segfault, and make

NasalSys.cxx more robust instead. The reason for the crash was that during
fgfs shutdown destroyed subsystems (GENERAL group) still need Nasal access
(for AI Model destruction listeners), but at that point globals->get_subsystem()
can't even deliver the "nasal" subsystem (INIT group). One way to solve that
problem would have been to replace  globals->get_subsystem("nasal") by
globals->get_subsystem_mgr()->get_group(SGSubsystemMgr::INIT)->get_subsystem("nasal"),
but Andy decided to store a pointer to the active "nasal" subsysten in
NasalSys.cxx instead, as the "nasal" subsystem needs to be accessed in
every single Nasal extension function, and multiple "nasal" subsystems are
out of the question, anyway.

src/Main/util.cxx

@@ -107,18 +107,6 @@ fgSetupWind (double min_hdg, double max_hdg, double speed, double gust)
 void
 fgExit (int status)
 {
-    // remove subsystems first, which need access to other subsystems in their
-    // destructors (e.g. "nasal")
-    SGSubsystem *sub;
-
-    sub = globals->get_subsystem("ai_model");
-    globals->get_subsystem_mgr()->get_group(SGSubsystemMgr::GENERAL)->remove_subsystem("ai_model");
-    delete sub;
-
-    sub = globals->get_subsystem("submodel_mgr");
-    globals->get_subsystem_mgr()->get_group(SGSubsystemMgr::GENERAL)->remove_subsystem("submodel_mgr");
-    delete sub;
-
 #ifdef OSG_LIBRARY_STATIC
     osgDB::Registry::instance( true);
 #endif
@@ -133,7 +121,7 @@ double
 fgGetLowPass (double current, double target, double timeratio)
 {
     if ( timeratio < 0.0 ) {
-	if ( timeratio < -1.0 ) {
+        if ( timeratio < -1.0 ) {
                                 // time went backwards; kill the filter
                 current = target;
         } else {

src/Scripting/NasalSys.cxx

@@ -22,6 +22,9 @@
 
 #include "NasalSys.hxx"
 
+static FGNasalSys* nasalSys = 0;
+
+
 // Read and return file contents in a single buffer.  Note use of
 // stat() to get the file size.  This is a win32 function, believe it
 // or not. :) Note the REALLY IMPORTANT use of the "b" flag to fopen.
@@ -52,6 +55,7 @@ static char* readfile(const char* file, int* lenOut)
 
 FGNasalSys::FGNasalSys()
 {
+    nasalSys = this;
     _context = 0;
     _globals = naNil();
     _gcHash = naNil();
@@ -82,6 +86,7 @@ naRef FGNasalSys::call(naRef code, naRef locals)
 
 FGNasalSys::~FGNasalSys()
 {
+    nasalSys = 0;
     map<int, FGNasalListener *>::iterator it, end = _listener.end();
     for(it = _listener.begin(); it != end; ++it)
         delete it->second;
@@ -254,8 +259,7 @@ static naRef f_fgcommand(naContext c, naRef me, int argc, naRef* args)
 // FGNasalSys::setTimer().  See there for docs.
 static naRef f_settimer(naContext c, naRef me, int argc, naRef* args)
 {
-    FGNasalSys* nasal = (FGNasalSys*)globals->get_subsystem("nasal");
-    nasal->setTimer(argc, args);
+    nasalSys->setTimer(argc, args);
     return naNil();
 }
 
@@ -263,24 +267,21 @@ static naRef f_settimer(naContext c, naRef me, int argc, naRef* args)
 // FGNasalSys::setListener().  See there for docs.
 static naRef f_setlistener(naContext c, naRef me, int argc, naRef* args)
 {
-    FGNasalSys* nasal = (FGNasalSys*)globals->get_subsystem("nasal");
-    return nasal->setListener(c, argc, args);
+    return nasalSys->setListener(c, argc, args);
 }
 
 // removelistener(int) extension function. Falls through to
 // FGNasalSys::removeListener(). See there for docs.
 static naRef f_removelistener(naContext c, naRef me, int argc, naRef* args)
 {
-    FGNasalSys* nasal = (FGNasalSys*)globals->get_subsystem("nasal");
-    return nasal->removeListener(c, argc, args);
+    return nasalSys->removeListener(c, argc, args);
 }
 
 // Returns a ghost handle to the argument to the currently executing
 // command
 static naRef f_cmdarg(naContext c, naRef me, int argc, naRef* args)
 {
-    FGNasalSys* nasal = (FGNasalSys*)globals->get_subsystem("nasal");
-    return nasal->cmdArgGhost();
+    return nasalSys->cmdArgGhost();
 }
 
 // Sets up a property interpolation.  The first argument is either a
@@ -777,8 +778,7 @@ void FGNasalModelData::modelLoaded(const string& path, SGPropertyNode *prop,
 
     _module = path;
     const char *s = load ? load->getStringValue() : "";
-    FGNasalSys *nas = (FGNasalSys *)globals->get_subsystem("nasal");
-    nas->createModule(_module.c_str(), _module.c_str(), s, strlen(s), _props);
+    nasalSys->createModule(_module.c_str(), _module.c_str(), s, strlen(s), _props);
 }
 
 FGNasalModelData::~FGNasalModelData()
@@ -786,8 +786,7 @@ FGNasalModelData::~FGNasalModelData()
     if(_module.empty())
         return;
 
-    FGNasalSys *nas = (FGNasalSys *)globals->get_subsystem("nasal");
-    if(!nas) {
+    if(!nasalSys) {
         SG_LOG(SG_NASAL, SG_ALERT, "Trying to run an <unload> script "
                 "without Nasal subsystem present.");
         return;
@@ -795,9 +794,9 @@ FGNasalModelData::~FGNasalModelData()
 
     if(_unload) {
         const char *s = _unload->getStringValue();
-        nas->createModule(_module.c_str(), _module.c_str(), s, strlen(s), _props);
+        nasalSys->createModule(_module.c_str(), _module.c_str(), s, strlen(s), _props);
     }
-    nas->deleteModule(_module.c_str());
+    nasalSys->deleteModule(_module.c_str());
 }