vdata_id	IN:	Vdata identifier returned by VSattach
	fieldname	IN:	Name of the field
	field_index	OUT:	Index of the field

	Purpose	Retrieves the index of a field within a vdata.
	Return value	Returns SUCCEED (or 0) if successful and FAIL (or -1) otherwise.
	Description	VSfindex retrieves the index, field_index, of the field with a name specified by the parameter fieldname, within the vdata identified by the parameter vdata_id.

	FORTRAN	integer function vsffidx(vdata_id, fieldname, field_index)
		integer vdata_id, field_index
		character*(*) fieldname