Coverity report bad_override

[danielwangksu]

Method "rviz::FailedDisplay::save" hides but does not override "rviz::Property::save" because some type qualifiers do not match.

rviz/src/rviz/failed_display.cpp

Lines 72 to 80 in f9b357f

	void FailedDisplay::save( Config config )
	{
	if( saved_config_.isValid() )
	{
	config.copy( saved_config_ );
	}
	}
	} // end namespace rviz

The function should add const keyword