fix auto-loading Doctrine mapping

Load the Doctrine mapping configuration automatically
when the db_driver is not configured as custom

Note. That is is only done for bundles that were build the generator
and old user-bundles need manual updating or manual configuring
improve CompilerPass registering

Reduce the amount of boilerplate and always works when Symfony 2.3 is
used (which is the minimum version)
bug #72 fix auto-loading Doctrine mapping (sstok)

This PR was merged into the master branch.

Discussion
----------

|Q            |A  |
|---          |---|
|Bug Fix?     |yes|
|New Feature? |no |
|BC Breaks?   |no |
|Deprecations?|no |
|Tests Pass?  |yes|
|Fixed Tickets|#71|
|License      |MIT|

 Sent using [Gush](https://github.com/gushphp/gush)

Commits
-------

2c458bfcdbdc382b9018ff81d4c3300a91b7f38a fix auto-loading Doctrine mapping

Load the Doctrine mapping configuration automatically
when the db_driver is not configured as custom

Note. That is is only done for bundles that were build the generator
and old user-bundles need manual updating or manual configuring (sstok)
9103d7bdfaf82e370e846640e5d94e3fc3d1734e improve CompilerPass registering

Reduce the amount of boilerplate and always works when Symfony 2.3 is
used (which is the minimum version) (sstok)