Ignore null value in comparison validators
fix some file mode bug 755->644
merged branch bronze1man/pr-file-mode (PR #8674)

This PR was merged into the 2.2 branch.

Discussion
----------

fix some file mode bug 755->644

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

Commits
-------

addd560 fix some file mode bug 755->644
Merge branch '2.2' into 2.3

* 2.2:
  fix some file mode bug 755->644
Fixed metadata serialization
Merge branch '2.0' into 2.1

* 2.0:
  Fixed metadata serialization
[Validator] fixed metadata serialization
Merge branch '2.1' into 2.2

* 2.1:
  [Validator] fixed metadata serialization
  Fixed metadata serialization
Merge branch '2.2' into 2.3

* 2.2:
  [Validator] fixed metadata serialization
  Fixed metadata serialization
added trusted hosts check
replaced deprecated Twig features
[Intl] Updated stubs to reflect ICU 51.2
Merge branch '2.0' into 2.1

* 2.0:
  added trusted hosts check

Conflicts:
	src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Configuration.php
	src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/ConfigurationTest.php
	src/Symfony/Component/HttpFoundation/Tests/RequestTest.php
Merge branch '2.1' into 2.2

* 2.1:
  added trusted hosts check

Conflicts:
	src/Symfony/Bundle/FrameworkBundle/Tests/DependencyInjection/ConfigurationTest.php
	src/Symfony/Component/HttpFoundation/Request.php
Merge branch '2.2' into 2.3

* 2.2:
  added trusted hosts check

Conflicts:
	src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php
updated CHANGELOG for 2.2.5
update CONTRIBUTORS for 2.2.5
updated VERSION for 2.2.5
bumped Symfony version to 2.2.6
updated CHANGELOG for 2.3.3