Update LdapAuthenticationProvider.php

Compatibility with Symfony 2.2
Update LdapAuthenticationProvider.php

Changes as https://github.com/liip/LiipOneallBundle/commit/648cbd8c965582e7b948a0ea427faab7344f5c8c#diff-1
Update LdapAuthenticationProvider.php

- Use AuthenticationServiceException instead of AuthenticationException
- Send (int)$repositoryProblem->getCode() instead of 0
Merge pull request #25 from DarwinOnLine/patch-2

Adapt AuthenticationServiceException signature to SF >= 2.2 preserving BC with SF <2.2 (Fixes #23)