vgroup_id	IN:	Vgroup identifier returned by Vattach
	tag_type	IN:	Type of the tag

	Purpose	Returns the number of tags of a given tag type in a vgroup.
	Return value	Returns 0 or the total number of tags if successful and FAIL (or -1) otherwise.
	Description	Vnrefs returns 0 or the number of tags having the type specified by the parameter tag_type in the vgroup identified by the parameter vgroup_id.
		See Appendix A, NCSA HDF Tags, in the HDF User's Guide, for a discussion of tag types.

	FORTRAN	integer function vnrefs(vgroup_id, tag_type)
		integer vgroup_id, tag_type