vdata_id	IN:	Vdata identifier returned by VSattach
	field_index	IN:	Vdata field index

	Purpose	Returns the size, as stored in memory, of a vdata field.
	Return value	Returns the vdata field size if successful and FAIL (or -1) otherwise.
	Description	VFfieldisize returns the size, as stored in memory, of a vdata field identified by the parameter field_index in the vdata identified by the parameter vdata_id.
		The value of the parameter field_index ranges from 0 to the total number of fields in the vdata - 1. The number of vdata fields is returned by VFnfields function.

	FORTRAN	integer function vffisiz(vdata_id, field_index)
		integer vdata_id, field_index