filename	IN:	Name of the file
	ref	IN:	Reference number to be used in next DFPgetpal call

	Purpose	Retrieves the reference number of the palette to be retrieved next by DFPgetpal.
	Return value	Returns SUCCEED (or 0) if the palette with the specified reference number exists and FAIL (or -1) otherwise.
	Description	Used to set the reference number of the next palette to be retrieved.

	FORTRAN	integer function dprref(filename, ref)
		character*(*) filename
		integer ref