by adding sleep-and-retries (max 4 times) if MASTER_POS_WAIT() returns NULL
in sync_with_master and sync_slave_with_master.
The problem showed up only today, in MySQL 5.0 in rpl_server_id2.test,
but may affect 4.x as well, so fixing it here. Note that I am also fixing
5.0 too, with the same exact patch, because I don't want to leave 5.0 broken
until the next 4.0->4.1->5.0 merge.


client/mysqltest.c:
  in sync_with_master (and sync_slave_with_master), if MASTER_POS_WAIT() returns NULL,
  it may be that the slave SQL thread did not have time to start yes, so we sleep
  1 sec and retry, 4 times at most.
mysql-test/r/rpl_server_id2.result:
  result update
mysql-test/t/rpl_server_id2.test:
  master_slave.inc already drops the table