return parameter for debug method

Added $return as 4th parameter to specify whether to return the debug text or print it. It works similar to print_r function
Update lib/Doctrine/Common/Util/Debug.php

coding style  fixes
Minor CS fixes
Swapping `$return` with `$echo` to fix return value consistency
Adding tests to validate features of DCOM-162
Merge pull request #306 from doctrine/DCOM-162

DCOM-162 - Returning the dumped value in `Doctrine\Common\Util\Debug::dump()`