file_id	IN:	File identifier returned by Hopen
	vdata_class	IN:	Class of the vdata

	Purpose	Returns the reference number of the first vdata with a given vdata class name
	Return value	Returns the reference number of the vdata if successful and 0 if the vdata is not found or an error occurs.
	Description	VSfindclass returns the reference number of the vdata with the class name specified by the parameter vdata_class in the file identified by the parameter file_id.

	FORTRAN	integer function vffcls(vdata_id, vdata_class)
		integer vdata_id
		character*(*) vdata_class