dollin' it up for Guilhem ;) -- test streamlined,
better comments, faster code, add'l assert.


mysql-test/r/binlog.result:
  Bug#22540: Incorrect value in column End_log_pos of SHOW BINLOG EVENTS using InnoDB
  
  streamlined test
mysql-test/t/binlog.test:
  Bug#22540: Incorrect value in column End_log_pos of SHOW BINLOG EVENTS using InnoDB
  
  streamlined test
sql/log.cc:
  Bug#22540: Incorrect value in column End_log_pos of SHOW BINLOG EVENTS using InnoDB
  
  comment clarified