gr_id	IN:	GR interface identifier returned by GRstart
	ri_name	IN:	Name of the raster image

	Purpose	Maps the name of a raster image to an index.
	Return value	Returns the index of the raster image if successful and FAIL (or -1) otherwise.
	Description	GRnametoindex returns, for the GR interface identified by the parameter gr_id, the index (index) of the raster image named gr_name.
		The value of index can be passed into GRselect to obtain the raster image identifier (ri_id).

	FORTRAN	integer function mgn2ndx(gr_id, gr_name)
		integer gr_id
		character*(*) gr_name