updated CHANGELOG for 2.3.23
update CONTRIBUTORS for 2.3.23
updated VERSION for 2.3.23
bumped Symfony version to 2.3.24
CS fixes
Removed unused imports
minor #12837 [2.3] CS Fixes And Removed Unused Imports (GrahamCampbell)

This PR was merged into the 2.3 branch.

Discussion
----------

[2.3] CS Fixes And Removed Unused Imports

| 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

##### This pull request fixes some cs issues in symfony 2.3.

As far as I understand, symfony's coding standards dictate that there should be no blank lines between imports and imports should not be prefixed with a slash. There are one or two other tiny fixes in here too.

Also, we should only import things that we actually *use*. :)

Commits
-------

0e4f0e7 Removed unused imports
0fc3369 CS fixes
[2.3] More cs fixes
minor #12840 [2.3] More cs fixes (GrahamCampbell)

This PR was squashed before being merged into the 2.3 branch (closes #12840).

Discussion
----------

[2.3] More cs fixes

| 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

##### This pull request fixes some more cs issues in symfony 2.3.

I should be done with cs fixes to the 2.3 branch now. Sorry I missed these in my last pull.

Commits
-------

b034b08 [2.3] More cs fixes
Merge branch '2.3' into 2.5

* 2.3:
  [2.3] More cs fixes
  Removed unused imports
  CS fixes
  bumped Symfony version to 2.3.24
  updated VERSION for 2.3.23
  update CONTRIBUTORS for 2.3.23
  updated CHANGELOG for 2.3.23

Conflicts:
	src/Symfony/Bundle/FrameworkBundle/EventListener/SessionListener.php
	src/Symfony/Bundle/SecurityBundle/DependencyInjection/MainConfiguration.php
	src/Symfony/Component/HttpKernel/Kernel.php
	src/Symfony/Component/HttpKernel/Tests/Bundle/BundleTest.php
	src/Symfony/Component/Routing/Matcher/Dumper/PhpMatcherDumper.php