Rename Qt-specific GetEventType() to start with "Qt" prefix

This avoids conflicts with another method with the same name defined in
generic wxGenericFileDirButton, which must neither override nor hide
this method of wxButton.

include/wx/qt/button.h

@@ -32,7 +32,7 @@ public:
    virtual wxWindow *SetDefault() wxOVERRIDE;
 
     // implementation only
-    virtual int GetEventType() const wxOVERRIDE { return wxEVT_BUTTON; }
+    virtual int QtGetEventType() const wxOVERRIDE { return wxEVT_BUTTON; }
 
 private:
     wxDECLARE_DYNAMIC_CLASS_NO_COPY(wxButton);