Overloads the keyPressEvent method to support backtab operations.
        
        :param      event | <QKeyPressEvent>

def keyPressEvent( self, event ):
        """
        Overloads the keyPressEvent method to support backtab operations.
        
        :param      event | <QKeyPressEvent>
        """
        if ( event.key() == Qt.Key_Backtab ):
            self.unindentSelection()
        else:
            super(XScintillaEdit, self).keyPressEvent(event)