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

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

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