- Fixed bug that we where using wrong checksum algorithm when using VARCHAR with fixed lenth rows
- Ensure in myisampack that HA_OPTION_NULL_FIELDS is set for tables with null fields.

mysql-test/r/myisampack.result:
  Updated results
mysql-test/t/myisampack.test:
  Added more tests
storage/myisam/mi_open.c:
  Use correct checksum algorithm when we have VARCHAR fields with fixed length records
storage/myisam/myisampack.c:
  Ensure HA_OPTION_NULL_FIELDS is set for tables with null fields.
  (This was not set by default for not compressed tables without checksums to keep MyISAM tables compatible with MySQL)