- when we don't have in_addr_t, use uint32.
- a forgotten initialization of slave_proxy_id in sql/log_event.cc (was not really "forgot", was
"we needn't init it there", but there was one case where we needed...).
- made slave_proxy_id always meaningful in THD and Log_event, so we can
rely more on it (no need to test if it's meaningful). THD::slave_proxy_id
is equal to THD::thread_id except for the slave SQL thread.
- clean up the slave's temporary table (i.e. free their memory) when slave
server shuts down.