The bug caused a reported index corruption in the cases when
key_cache_block_size was not a multiple of myisam_block_size,
e.g. when key_cache_block_size=1536 while myisam_block_size=1024.


mysql-test/r/key_cache.result:
  Added a test case for bug #19079.
mysql-test/t/key_cache.test:
  Added a test case for bug #19079.