Unit test fixes

[Validator][Debug] Fixing unit tests

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        | 
They are not, however it seems to me that it corrupts the error handlers for other tests.
It overrides the PHPUnit error handler and for example breaks the tests where a catchable fatal error is meant to be caught as a PHPUnit_Framework_Exception for testing array typehinting and checking the emission of strict standard errors (`Symfony\Component\Validator\Tests\Mapping\Loader\StaticMethodLoaderTest::testLoadClassMetadataIgnoresAbstractMethods`)
(Ubuntu 14.04.1 LTS, PHP 5.5.9-1ubuntu4.4, PHPUnit 3.7.28)