Changed Rotate_log_event::exec_event() to not increment positions when the
event is seen in the middle of a transaction.


mysql-test/r/rpl_relayrotate.result:
  remove timeout which was too short for Valgrind
mysql-test/r/rpl_until.result:
  updated error message
mysql-test/t/rpl_relayrotate.test:
  removed timeout which was too short for Valgrind
sql/log_event.cc:
  Fix for a rpl_relayrotate failure. The problem was that Rotate_log_event::exec_event()
  believed that the relay log was corrupted. Fixed it by moving the test for
  corruption to Start_log_event::exec_event(). 
  Changed Rotate_log_event::exec_event() to not increment positions when the
  event is seen in the middle of a transaction (that was an old bug found by
  chance :)