Hook in the fgOSExit() function.

src/Main/fg_os.cxx

@@ -139,6 +139,11 @@ void fgOSMainLoop()
     glutMainLoop();
 }
 
+void fgOSExit(int code)
+{
+    exit(code);
+}
+
 static int CurrentCursor = MOUSE_CURSOR_POINTER;
 
 int fgGetMouseCursor()

src/Main/fg_os.hxx

@@ -46,6 +46,7 @@ void fgOSOpenWindow(int w, int h, int bpp, bool alpha, bool stencil,
                     bool fullscreen);
 void fgOSFullScreen();
 void fgOSMainLoop();
+void fgOSExit(int code);
 
 void fgSetMouseCursor(int cursor);
 int  fgGetMouseCursor();

src/Main/main.cxx

@@ -1447,6 +1447,7 @@ void fgReshape( int width, int height ) {
 // which happens in the sound manager destructor.
 void fgExitCleanup() {
     delete globals;
+    fgOSExit(0);
 }