filename	IN:	Name of the file
	tag	IN:	Tag of the data object assigned the description
	ref	IN:	Reference number of the data object assigned the description

	Purpose	Retrieves the length of a description of the data object with the given tag and reference number.
	Return value	Returns the length of a description if successful and FAIL (or -1) otherwise.
	Description	This routine should be used to insure that there is enough space allocated for a description before actually reading it.

	FORTRAN	integer function dagdlen(filename, tag, ref)
		character*(*) filename
		integer tag, ref