[GH-314] [WIP] Doctrine\Common metadata drivers reuse

This issue is created automatically through a Github pull request on behalf of Ocramius:

Url: https://github.com/doctrine/doctrine2/pull/314

Message:

This PR is strictly related with https://github.com/doctrine/common/pull/98 and tests won't pass until the doctrine-common submodule points to a merged version of it (will do so later, so please don't merge now ).

Basically, I just stripped any code duplicate of what already available in dcom master under Doctrine\Common\Persistence\Mapping\Driver.

Tests are OK on my environment when using the new commons submodule.

(This is a cleanup for #263, where I sadly did pull from the remote branch after rebasing)

Tests are still failing.