Allow Doctrine 2.4 to be installed

The commit https://github.com/symfony/symfony-standard/commit/0cafa504b6d1235c901d127da01c996219341e6c#diff-b5d0ee8c97c7abd7e3fa29b9a27d1780, lets Doctrine 2.4 installable

But it has been performed only on `master`, `2.4`

Any reason why it shouldn't also be backported to last stable version of `symfony-standard` (`2.3`) ?