removed defaults from PHPUnit configuration
updated VERSION for 2.5.1
bumped Symfony version to 2.4.8
bumped Symfony version to 2.5.2
minor #11344 remove defaults from PHPUnit configuration (craue)

This PR was merged into the 2.3 branch.

Discussion
----------

remove defaults from PHPUnit configuration

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | --
| License       | MIT
| Doc PR        | --

Follow-up to #11329.

Commits
-------

afc4930 removed defaults from PHPUnit configuration
Merge branch '2.3' into 2.4

* 2.3:
  fixed CS
  [HttpFoundation] Remove content-related headers if content is empty
  removed defaults from PHPUnit configuration
Merge branch '2.4' into 2.5

* 2.4:
  added missing test
  fixed CS
  [HttpFoundation] Remove content-related headers if content is empty
  bumped Symfony version to 2.4.8
  removed defaults from PHPUnit configuration

Conflicts:
	src/Symfony/Component/HttpKernel/Kernel.php
Merge branch '2.5'

* 2.5:
  added missing test
  fixed CS
  [HttpFoundation] Remove content-related headers if content is empty
  bumped Symfony version to 2.5.2
  bumped Symfony version to 2.4.8
  updated VERSION for 2.5.1
  updated CHANGELOG for 2.5.1
  removed defaults from PHPUnit configuration

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