Defined stable version point of Doctrine.

As per @stof comments, here is the stable minimum version definition for Doctrine libraries on master.

```
| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | no
```

PS: Broken tests are totally unrelated with this patch. It seems there's an issue with Locale component that fails Brazilian assertions... what a lucky situation. =) Will fix the broken tests of Locale in a few.