DBManager: Fixed various backward compatibility issues.

* The version checks didn't like multiple digits in the version major.

* Added potential support for restoring of old-style BACKUPs in
  MariaDB/MySQL 5.5 and later.
Added compat-level for Roxen 5.5.
Testsuite: Support MariaDB/MySQL 5.5 and later.

The mysql_fix_privilege_tables.sql script is no more in MariaSB/Mysql
5.5 and later. Test for the existence of its replacement instead.
Version bumped to 5.5.11 by buildsystem.