Don't update if column width didn't change in generic wxDataViewCtrl

Avoid calling UpdateDisplay() unnecessarily if the column width didn't really
change. This doesn't result in anything really bad happening right now, but it
could easily result in an infinite stream of updates if the code were only
slightly different and it just seems useless to do it.

include/wx/generic/dataview.h

@@ -63,10 +63,13 @@ public:
     }
 
     virtual void SetWidth(int width) wxOVERRIDE
+    {
+        if ( width != m_width )
         {
             m_width = width;
             UpdateDisplay();
         }
+    }
     virtual int GetWidth() const wxOVERRIDE;
 
     virtual void SetMinWidth(int minWidth) wxOVERRIDE