* Updated RESET SLAVE to reset Master/Slave_last_event_time

 * Updated SHOW ALL SLAVES STATUS to treat Master and Slave NULL
   times separately

 * Updated SQL thread's update on first transaction read-in to
   only update Slave_last_event_time on group events

 * Added test cases for
   - Ensuring (Master|Slave)_last_event_time is updated at the
     correct place
   - Ensuring the first event read by the SQL thread will update
     Slave_last_event_time
   - A parallel delayed replica updates the new fields
     correctly