add a missing removeObserver: to the message window controller

the last commit ensured that the drag overlay window resized when not window, which led to inaccurate sizes when exposé-d

macosx/MessageWindowController.m

@@ -50,6 +50,8 @@
 
 - (void) dealloc
 {
+    [[NSNotificationCenter defaultCenter] removeObserver: self];
+    
     [fTimer invalidate];
     [fLock release];