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/r/rpl000015.result:
  result update
mysql-test/r/rpl_empty_master_crash.result:
  result update
mysql-test/r/rpl_error_ignored_table.result:
  result update
mysql-test/r/rpl_flush_log_loop.result:
  result update
mysql-test/r/rpl_loaddata.result:
  result update
mysql-test/r/rpl_log.result:
  result update
mysql-test/r/rpl_log_pos.result:
  result update
mysql-test/r/rpl_max_relay_size.result:
  result update
mysql-test/r/rpl_redirect.result:
  result update
mysql-test/r/rpl_replicate_do.result:
  result update
mysql-test/r/rpl_reset_slave.result:
  result update
mysql-test/r/rpl_rotate_logs.result:
  result update
mysql-test/r/rpl_trunc_binlog.result:
  result update
mysql-test/r/rpl_until.result:
  result update
mysql-test/t/rpl000015.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_empty_master_crash.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_error_ignored_table.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_flush_log_loop.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_loaddata.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_log.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_log_pos.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_max_relay_size.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_openssl.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_redirect.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_replicate_do.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_reset_slave.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_rotate_logs.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_trunc_binlog.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
mysql-test/t/rpl_until.test:
  update to be independant of the new column Seconds_behind_master in SHOW SLAVE STATUS
sql/log_event.cc:
  when the SQL thread executes an event, we record its timestamp
sql/slave.cc:
  in check_master_version() we know read the master's clock, to know the clock difference
  with the slave.
  In show_master_info() we send the state of the I/O thread, and compute the number of
  seconds by which the slave is late.
sql/slave.h:
  timestamp of the last master's event executed by the SQL thread,
  and difference between the clocks of the master and slave.
sql/sql_repl.cc:
  clear the Seconds_behind_master column of SHOW SLAVE STATUS when RESET SLAVE or CHANGE MASTER.

sql/sql_repl.cc

@@ -878,7 +878,11 @@ int reset_slave(THD *thd, MASTER_INFO* mi)
     STATUS; before doing START SLAVE;
   */
   init_master_info_with_options(mi);
-  clear_last_slave_error(&mi->rli);
+  /* 
+     Reset errors, and master timestamp (the idea is that we forget about the
+     old master).
+  */
+  clear_slave_error_timestamp(&mi->rli);
   clear_until_condition(&mi->rli);
   
   // close master_info_file, relay_log_info_file, set mi->inited=rli->inited=0
@@ -1092,8 +1096,8 @@ int change_master(THD* thd, MASTER_INFO* mi)
 
   pthread_mutex_lock(&mi->rli.data_lock);
   mi->rli.abort_pos_wait++; /* for MASTER_POS_WAIT() to abort */
-  /* Clear the error, for a clean start. */
-  clear_last_slave_error(&mi->rli);
+  /* Clear the errors, for a clean start, and master timestamp */
+  clear_slave_error_timestamp(&mi->rli);
   clear_until_condition(&mi->rli);
   /*
     If we don't write new coordinates to disk now, then old will remain in