Final push for WL#1098:

"Add a column "Timestamp_of_last_master_event_executed" in SHOW SLAVE STATUS".
Finally this is adding
- Slave_IO_State (a copy of the State column of SHOW PROCESSLIST for the I/O thread,
so that the users, most of the time, has enough info with only SHOW SLAVE STATUS).
- Seconds_behind_master. When the slave connects to the master it does SELECT UNIX_TIMESTAMP()
on the master, computes the absolute difference between the master's and the slave's clock.
It records the timestamp of the last event executed by the SQL thread, and does a
small computation to find the number of seconds by which the slave is late.

mysql-test/t/rpl_trunc_binlog.test

@@ -21,6 +21,7 @@ start slave;
 # can't sync_with_master so we must sleep
 sleep 3;
 --replace_result $MASTER_MYPORT MASTER_PORT
+--replace_column 33 #
 show slave status;
 connection master;
 reset master;