[paragui-users] a few changes to PG_FileSelector

[Keith Swyer]

protected:
 //! file selected event
 /*!
  @param filename name of current filename selected
 */
 virtual bool eventFileSelected(const char* filename);
 //! dir select event
 /*!
  @param dirname name of current dirname selected
 */
 virtual bool eventDirEntered(const char* dirname);
 //! filter select event
 /*!
  @param filter name of current filter selected
 */
 virtual bool eventFilterSelected(const char* filter);
  
 PARAGUI_CALLBACK(filter_select_handler);
 PARAGUI_CALLBACK(file_select_handler);
 PARAGUI_CALLBACK(dir_select_handler);