{
{    The purpose of this request is to get a prefix from a message.  The prefix
{ may consist of the entire message.  This request does not change the message.
{
{    NOTE:  If the message identifier is invalid, prefix is NIL, or prefix
{          length is zero, a system error ('Buffer Manager Caller') will occur.
{
{       NLP$BM_GET_MESSAGE_PREFIX (PREFIX, PREFIX_LENGTH, MESSAGE_ID, STATUS)
{
{ PREFIX: (input)  This parameter specifies the address where the prefix is to
{       be stored.
{
{ PREFIX_LENGTH: (input)  This parameter specifies the length of the prefix to
{       be obtained.
{
{ MESSAGE_ID: (input)  This parameter specifies the identifier of the message
{       from which the prefix is to be obtained.
{
{ STATUS: (output) This parameter specifies the request status.
{       CONDITIONS:
{             nae$insufficent_data
{
