previous correction didn't. make sure "tail" is fixed up
when filling cache several times; rework formulae.


mysql-test/r/binlog.result:
  Bug#22540: Incorrect value in column End_log_pos of SHOW BINLOG EVENTS using InnoDB
  
  show that fix for absolute end_log_pos in binlog also
  works when cache is read several times and headers are
  split across that boundary
mysql-test/t/binlog.test:
  Bug#22540: Incorrect value in column End_log_pos of SHOW BINLOG EVENTS using InnoDB
  
  show that fix for absolute end_log_pos in binlog also
  works when cache is read several times and headers are
  split across that boundary