ErrorHandlerTest: restore_error_handler() on assertion failure
minor #9742 ErrorHandlerTest: restore_error_handler() on assertion failure (nicolas-grekas)

This PR was submitted for the 2.4-dev branch but it was merged into the 2.4 branch instead (closes #9742).

Discussion
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ErrorHandlerTest: restore_error_handler() on assertion failure

Before the patch, if any test fail in src/Symfony/Component/Debug/Tests/ErrorHandlerTest.php,
phpunit's error handler is not correctly restored.
When running a test batch, this breaks other tests that rely on its behavior (@expectedException PHPUnit_Framework_Error)

Commits
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a6ed37c ErrorHandlerTest: restore_error_handler() on assertion failure
[Debug] fixed tests
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
fixed CS
Merge branch '2.3' into 2.4

* 2.3:
  fixed CS
fixed CS
Merge branch '2.4'

* 2.4:
  fixed CS
  fixed CS
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