macosx/framework: Make sure the nsobject drawable is never used after being freed.

This issue was pointed out by Sébastien Zwickert.

We ensure this by two things:
- Retaining it by the media player and ensuring we are effectively stopped when releasing it. (ie, no one will use the drawable from now on).
- Retaining it during the life span of the vout. After a stop, the drawable might still be in the progress of receiving the notification of the vout removal, so we need it not to be freed during this period of time.
An alternative would be to create a protocol between drawable->vout to unregister the drawable.

Headers/Public/VLCMediaPlayer.h

@@ -83,6 +83,7 @@ extern NSString * VLCMediaPlayerStateToString(VLCMediaPlayerState state);
     VLCTime * cachedTime;               //< Cached time of the media being played
     VLCMediaPlayerState cachedState;    //< Cached state of the media being played
     float position;                     //< The position of the media being played
+    id drawable;                        //< The drawable associated to this media player
 }
 
 /* Initializers */

Sources/VLCMediaPlayer.m

@@ -192,15 +192,23 @@ static void HandleMediaInstanceStateChanged(const libvlc_event_t * event, void *
 
 - (void)dealloc
 {
+    NSAssert(libvlc_media_player_get_state(instance, NULL) == libvlc_Stopped, @"You released the media player before ensuring that it is stopped");
+
     // Always get rid of the delegate first so we can stop sending messages to it
     // TODO: Should we tell the delegate that we're shutting down?
     delegate = nil;
 
-    libvlc_media_player_release((libvlc_media_player_t *)instance);
+    // Clear our drawable as we are going to release it, we don't
+    // want the core to use it from this point. This won't happen as
+    // the media player must be stopped.
+    libvlc_media_player_set_nsobject(instance, nil, NULL);
+
+    libvlc_media_player_release(instance);
     
     // Get rid of everything else
     [media release];
     [cachedTime release];
+    [drawable release];
 
     [super dealloc];
 }
@@ -503,16 +511,6 @@ static void HandleMediaInstanceStateChanged(const libvlc_event_t * event, void *
 
 - (void)stop
 {
-    if( 0 && [NSThread isMainThread] )
-    {
-        /* Hack because we create a dead lock here, when the vout is stopped
-         * and tries to recontact us on the main thread */
-        /* FIXME: to do this properly we need to do some locking. We may want 
-         * to move that to libvlc */
-        [self performSelectorInBackground:@selector(stop) withObject:nil];
-        return;
-    }
-    
     libvlc_exception_t ex;
     libvlc_exception_init( &ex );
     libvlc_media_player_stop((libvlc_media_player_t *)instance, &ex);