The check for rotate event conditions was wrong which led to false error
message about unexpected binlog file and position combinations.
The position of the last event was reset every time a file was opened which
caused problems when the binlog file was rotated. The slave's current positions
were compared to the position where the last event started and because the
last_event_pos variable didn't point to the rotate event of the previous binlog,
the slave's never got the rotate event.
6988c0bfed