Since 4.1 keys are compared with trailing spaces. 
Thus, a "x " key can be inserted between a couple of "x" keys.
The existing code did not take this into account. Though the
comments in the code claimed it did.


myisam/mi_search.c:
  Bug#9188 - Corruption Can't open file: 'table.MYI' (errno: 145)
  Fixed some function comments.
  In the case when we insert a different key between two identical keys,
  the difference must be additional spaces. In this case the prefix is 
  the same as that of the new key instead of the (zero) remaining length.
myisam/mi_write.c:
  Bug#9188 - Corruption Can't open file: 'table.MYI' (errno: 145)
  Fixed a function comment.
mysql-test/r/myisam.result:
  Bug#9188 - Corruption Can't open file: 'table.MYI' (errno: 145)
  The test result.
mysql-test/t/myisam.test:
  Bug#9188 - Corruption Can't open file: 'table.MYI' (errno: 145)
  The test case.