Allow symfony >= 2.3

This required a small tweak to the tests as
Symfony\Component\PropertyAccess\Exception\PropertyAccessDeniedException
 has been removed in 2.3
Merge pull request #282 from tommygnr/symfony2.3

Allow symfony >= 2.3
Expect a more specific PropertyAccess exception

RuntimeException is the nearest common ancestor of the PropertyAccessDeniedException (removed in 2.3) and NoSuchPropertyException.

See: symfony/symfony@2a666cb7c3ecbaa6226e5a9da0476b10b6e997db