filename	IN:	Name of the HDF file
	ref	IN:	Reference number for next DFSDgetdata call

	Purpose	Specifies the reference number for the dataset to be read during the next read operation.
	Return value	Returns SUCCEED (or 0) if successful and FAIL (or -1) otherwise.
	Description	This routine is commonly used in conjunction with DFANgetlablist, which returns a list of labels for a given tag together with their reference numbers. It provides a sort of random access to scientific datasets.
		There is no guarantee that reference numbers appear in sequence in an HDF file, so it is not generally safe to assume that a reference number is an index number of a scientific dataset.

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