Merge pull request #2101 from mockingbird/fix-cpwindow-setcontentview-check

Have CPWindow setContentView check that the new view is not the same as the existing content view

AppKit/CPWindow/CPWindow.j

@@ -1131,7 +1131,7 @@ CPTexturedBackgroundWindowMask
 */
 - (void)setContentView:(CPView)aView
 {
-    if (_contentView)
+    if (_contentView && _contentView !== aView)
         [_contentView removeFromSuperview];
 
     var bounds = CGRectMake(0.0, 0.0, CGRectGetWidth(_frame), CGRectGetHeight(_frame));