file_id	IN:	File identifier returned by Hopen
	vgroup_ref	IN:	Reference number of the current vgroup

	Purpose	Returns the reference number of the next vgroup.
	Return value	Returns the reference number of the next vgroup if successful and FAIL (or -1) otherwise.
	Description	Vgetid sequentially searches the file identified by the parameter file_id and returns the reference number of the vgroup following the vgroup that has the reference number specified by the parameter vgroup_ref.
		The search is initiated by calling this routine with a vgroup_ref value of -1. This will return the reference number of the first vgroup in the file. Searching past the last vgroup in the file will cause Vgetid to return FAIL (or -1).

	FORTRAN	integer function vfgid(file_id, vgroup_ref)
		integer file_id, vgroup_ref