vdata_id	IN:	Vdata identifier returned by VSattach
	field_name_list	OUT:	Field name list

	Purpose	Retrieves the field names of all of the fields in a vdata.
	Return value	Returns the number of fields in the vdata if successful and FAIL (or -1) otherwise.
	Description	VSgetfields retrieves the names of the fields in the vdata identified by the parameter vdata_id into the buffer field_name_list.
		The parameter field_name_list is a character string containing a comma-separated list of names (e.g., "PX,PY,PZ" in C or `PX,PY,PZ' in Fortran).

	FORTRAN	integer function vsfgfld(vdata_id, field_name_list)
		integer vdata_id
		character*(*) field_name_list