This patch adds corrections to the original patch
submitted 2009-04-08 (http://lists.mysql.com/commits/71607):

- fixed that the original patch didn't work because of an
  incorrect condition;
- added a test case.

mysql-test/r/upgrade.result:
  Bug#37631 Incorrect key file for table after upgrading from 5.0 to 5.1
  
  Result file for test case
mysql-test/std_data/bug37631.MYD:
  Bug#37631 Incorrect key file for table after upgrading from 5.0 to 5.1
  
  table created in mysql 4.0
mysql-test/std_data/bug37631.MYI:
  Bug#37631 Incorrect key file for table after upgrading from 5.0 to 5.1
  
  table created in mysql 4.0
mysql-test/std_data/bug37631.frm:
  Bug#37631 Incorrect key file for table after upgrading from 5.0 to 5.1
  
  table created in mysql 4.0
mysql-test/t/upgrade.test:
  Bug#37631 Incorrect key file for table after upgrading from 5.0 to 5.1
  
  Adds test for checking that upgrade works
  on a table which is created by a mysql
  server version <= 4.0.
storage/myisam/ha_myisam.cc:
  Bug#37631 Incorrect key file for table after upgrading from 5.0 to 5.1
  
  Fix the conformance checker to relax checking
  for the correct version of the tables (for tables
  created by mysql server version <= 4.0)