When compiling with a default key block size greater than the
smallest key block size used in a table, checking that table
failed with bogus errors. The table was marked corrupt. This
affected myisamchk and the server.

The problem was that the default key block size was used at
some places where sizes less or equal to the block size of the
index in check was required.

We do now use the key block size of the particular index
when checking.

A test case is available for later versions only.