backport mouse capture fixes 00cc023 and dc555a9

this change was supposed to be part of 69c7a8c405

include/wx/gtk/window.h

@@ -185,6 +185,7 @@ public:
     // This is called when capture is taken from the window. It will
     // fire off capture lost events.
     void GTKReleaseMouseAndNotify();
+    static void GTKHandleCaptureLost();
 
     GdkWindow* GTKGetDrawingWindow() const;