Removed the assumption of a certain key order.
Since 4.1, keys are padded with blanks for comparison.
Hence, shorter keys sort behind longer keys, if the
data bytes have values below BLANK.


mysql-test/r/key.result:
  BUG#6151 - myisam index corruption.
  The test results.
mysql-test/t/key.test:
  BUG#6151 - myisam index corruption.
  Added the test case as derived from the original data.