Handle GUI quit correctly.

stepmania/PBProject/SMMain.mm

@@ -21,6 +21,7 @@
 }
 - (id) initWithArgc:(int)argc argv:(char **)argv;
 - (void) startGame:(id)sender;
+- (NSApplicationTerminateReply) applicationShouldTerminate:(NSApplication *)sender;
 @end
 
 
@@ -29,11 +30,6 @@
 {
 	ArchHooks::SetToggleWindowed();
 }
-// Invoked from the Quit menu item.
-- (void)terminate:(id)sender
-{
-	ArchHooks::SetUserQuit();
-}
 
 - (void)sendEvent:(NSEvent *)event
 {
@@ -66,6 +62,12 @@
 {
 	[NSThread detachNewThreadSelector:@selector(startGame:) toTarget:self withObject:nil];
 }
+
+- (NSApplicationTerminateReply) applicationShouldTerminate:(NSApplication *)sender
+{
+	ArchHooks::SetUserQuit();
+	return NSTerminateCancel;
+}
 @end
 
 static void HandleNSException( NSException *exception )