Reset the box model to content-box in the web debug toolbar

This makes the styles compatible with CSS frameworks changing the box
model to box-sizing using a universal selector (Bootstrap 3 for instance).
Merge branch '2.3' into 2.4

* 2.3:
  Fixed typo
  [validator] throw an exception if isn't an instance of ConstraintValidatorInterface.
  Reset the box model to content-box in the web debug toolbar
  [FrameworkBundle] Allowed "0" as a checkbox value in the php template.
  raising delta on stopwatch as travis really breaks with less than 35
  Switched to correct gender of "Token"
  fixed typos in several translations
  [HttpKernel] use static late binding when dumping out container
Merge branch '2.4'

* 2.4:
  [Debug] fixed tests
  ErrorHandlerTest: restore_error_handler() on assertion failure
  Fixed typo
  [validator] throw an exception if isn't an instance of ConstraintValidatorInterface.
  Reset the box model to content-box in the web debug toolbar
  [FrameworkBundle] Allowed "0" as a checkbox value in the php template.
  raising delta on stopwatch as travis really breaks with less than 35
  Switched to correct gender of "Token"
  bumped Symfony version to 2.4.1
  updated VERSION for 2.4.0
  updated CHANGELOG for 2.4.0
  fixed typos in several translations
  [HttpKernel] use static late binding when dumping out container

Conflicts:
	src/Symfony/Component/HttpKernel/Kernel.php