If database tests cannot be run the error message is ambigous. This
commit makes it clearer:
- whether the supplied dbms is supported by us
- which dbms are supported by us
- whether the required PDO extension is loaded
PHPBB3-10043
Move most of the methods to a separate connection manager class. The
test case creates a manager to handle database creation, schema loading
and more. Most of the methods could be simplified because they can
access shared pdo, config and dbms data.
PHPBB3-10043
