{   This procedure checks whether or not a tapemark is the next thing on the
{ tape, without actually reading the block via bap$tape_bm_read_next_block.
{ This allows determination of end of volume on unlabelled tapes.
{
{ NOTE:  If necessary, this procedure will read ahead on the tape.  This can
{       impact performance for extremely large blocks.  This procedure should
{       be called only when necessary, NOT after every
{       bap$tape_bm_read_next_block call.
{
{       BAP$TAPE_BM_TAPEMARK_CHECK(FILE_IDENTIFIER, TAPEMARK_NEXT, STATUS)
{
{   FILE_IDENTIFIER (Input):  The file identifier for the file.
{
{ TAPEMARK_NEXT: (output)  TRUE if the next block is a tapemark.  FALSE if it
{       is anything else, including a read error.
{
{ STATUS: (Output) Request status.
