Don't call dispatch_release if dispatch_queue_t is declared as Objective-C object.

@@ -65,7 +65,9 @@
         _memoryCache = nil;
     });
     
+#if ! OS_OBJECT_USE_OBJC
     dispatch_release(_memoryCacheQueue);
+#endif
 }
 
 - (void)didReceiveMemoryWarning

@@ -132,7 +132,9 @@
          _tileCaches = nil;
     });
     
+#if ! OS_OBJECT_USE_OBJC
     dispatch_release(_tileCacheQueue);
+#endif
 }
 
 - (void)addCache:(id <RMTileCache>)cache