[FrameworkBundle] Fixed validator factory definition when the Validator API is "auto" for PHP < 5.3.9
Merge branch '2.5'

* 2.5:
  [Validator] Fixed missing use statements
  [Validators] Fixed failing tests requiring ICU 52.1 which are skipped otherwise
  [FrameworkBundle] Fixed validator factory definition when the Validator API is "auto" for PHP < 5.3.9
  return empty metadata collection if none do exist