CSRF warning docs on Request::enableHttpMethodParameterOverride()

[HttpFoundation] fixed the docs so that it gives some explanation about how you are vulnerable to CSRF when you enable the httpMethodeParameterOverride
Removed fixed height from profiler resume box.
[Form] fix form handling with unconventional request methods like OPTIONS
[Config] fix filelocator with empty name
[DependencyInjection] use inheritdoc for loaders
[Validator] Fixed Regex::getHtmlPattern() to work with complex and negated patterns
[VarDumper] fix control chars styling
[EventDispatcher] perf optim
[HttpKernel] fix DebugHandlersListener
[Form] Fixed usage of "name" variable in form_start block
updated CHANGELOG for 2.3.21
update CONTRIBUTORS for 2.3.21
updated VERSION for 2.3.21
bumped Symfony version to 2.3.22
updated CHANGELOG for 2.5.6
updated VERSION for 2.5.6
bumped Symfony version to 2.5.7
Ensure that Twig form themes are always a list, not a hashmap

array_unique does not reindex arrays when deleting keys.
bug #12308 Ensure that Twig form themes are always a list, not a hashmap (stof)

This PR was merged into the 2.6-dev branch.

Discussion
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Ensure that Twig form themes are always a list, not a hashmap

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #12305
| License       | MIT
| Doc PR        | n/a

array_unique does not reindex arrays when deleting keys.

Commits
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2a19cd8 Ensure that Twig form themes are always a list, not a hashmap
Improved the phpdoc for security token classes