vgroup_id	IN:	Vgroup identifier returned by Vattach
	index	IN:	Index of the object in the vgroup
	tag	OUT:	Tag of the object
	ref	OUT:	Reference number of the object

	Purpose	Retrieves the tag/reference number pair of an object given its index within a vgroup.
	Return value	Returns SUCCEED (or 0) if successful and FAIL (or -1) otherwise.
	Description	Vgettagref retrieves the tag/reference number pair of the object specified by its index, index, within the vgroup identified by the parameter vgroup_id. Note that this routine is different from Vgettagrefs, which retrieves the tag/reference number pairs of a number of objects.
		The valid values of index range from 0 to the total number of objects in the vgroup - 1. The total number of objects in the vgroup can be obtained using Vinquire.
		The tag is stored in the buffer tag and the reference number is stored in the buffer ref.

	FORTRAN	integer function vfgttr(vgroup_id, index, tag, ref)
		integer vgroup_id, index
		integer tag, ref