This commit fixes warning like one reported below occuring when imlementing
custom event translators:


```
In file included from /home/jcfr/Projects/Slicer/Libs/MRML/Widgets/qMRMLNodeComboBoxEventTranslator.h:28:0,
                 from /home/jcfr/Projects/Slicer/Base/QTGUI/qSlicerApplication.cxx:84:
/home/jcfr/Projects/Slicer-Release/CTK-build/QtTesting/pqWidgetEventTranslator.h:62:16: warning: ‘virtual bool pqWidgetEventTranslator::translateEvent(QObject*, QEvent*, int, bool&)’ was hidden [-Woverloaded-virtual]
   virtual bool translateEvent(QObject* object, QEvent* event, int eventType, bool& error);
                ^
In file included from /home/jcfr/Projects/Slicer/Base/QTGUI/qSlicerApplication.cxx:84:0:
/home/jcfr/Projects/Slicer/Libs/MRML/Widgets/qMRMLNodeComboBoxEventTranslator.h:43:16: warning:   by ‘virtual bool qMRMLNodeComboBoxEventTranslator::translateEvent(QObject*, QEvent*, bool&)’ [-Woverloaded-virtual]
   virtual bool tra...