Add symfony-bin-dir (bin/console) support - FIXES: #245,#246.

Quickly added `symfony-bin-dir` support. Hope that helps prevent further issues.

It's basically a simplified version of [sstok's implementation](https://github.com/sstok/SpBowerBundle/commit/a82fcb4badf6f560482b274f3a7c267d47b5c92c) for SpBowerBundle.

The `symfony-bin-dir` key gets added in SensioDistributionBundle's [`ScriptHandler::defineDirectoryStructure`](https://github.com/sensiolabs/SensioDistributionBundle/blob/master/Composer/ScriptHandler.php#L53).