"If 2 master threads with same-name temp table, slave makes bad binlog"
and (two birds with one stone) for
BUG#1240 "slave of slave breaks when STOP SLAVE was issud on parent slave
and temp tables".

Here is the design change:
in a slave running with --log-slave-updates, events are now logged with the
thread id they had on the master. So no more id conflicts between master threads,
but introduces id conflicts between one master thread and one normal 
client thread connected to the slave. This is solved by storing the server id
in the temp table's name.

New test which requires mysql-test-run to be run with --manager,
otherwise it will be skipped.

Undoing a Monty's change (hum, a chill runs down my spine ;) which was
"Cleanup temporary tables when slave ends" in ChangeSet 1.1572.1.1.