When using a PDOConnection and the Portability wrapper, the default value \PDO::CASE_NATURAL int(0) and PHP constant CASE_LOWER int(0) got mixed up.

This enables a more natural way of interacting with result sets,
and re-introduces in Doctrine DBAL a feature that has been available
in PDO from the begining.

DDC-217 - Refactor result cache again to be much simpler, previous approach was too complicated and something like this needs longer testing. Now only caching the full result.

[DBAL-56] Add portability wrapping layer porting MDB2 functionality to fix case, rtrim strings and convert empty strings to null.