Throw exception when unable to normalize embedded object

Added a check to ensure that injected serializer of the
GetSetMethodNormalizer is a normalizer before normalizing object value.
Merge branch '2.4'

* 2.4:
  [Form][2.3] Fixes empty file-inputs getting treated as extra field.
  changed some PHPUnit assertions to more specific ones
  fixed Kernel::stripComments() normalizing new-lines
  added a BC comment
  Update FileLoader to fix issue #10339
  bumped Symfony version to 2.3.12
  updated VERSION for 2.3.11
  update CONTRIBUTORS for 2.3.11
  updated CHANGELOG for 2.3.11
  Throw exception when unable to normalize embedded object
  Fixed evaluation of short circuit operators
  Follow-up to #10312: Fixed minor performance related issues in Yaml\Inline.
  [2.4][HttpKernel] Fix issue #10209 When the profiler has `only_exception` option activated and a subrequest throw an exception, the parent profile cannot be found.