Add check to Store::unlock to ensure file exists

Fix indentation and shorten code
updated VERSION for 2.0.18
bumped Symfony version to 2.0.19-DEV
merged branch jonathaningram/issue_5375 (PR #5376)

This PR was merged into the 2.0 branch.

Commits
-------

a094f7e Add check to Store::unlock to ensure file exists

Discussion
----------

[2.0] [HttpKernel] Add check to Store::unlock to ensure file exists

Bug fix: yes
Feature addition: no
Backwards compatibility break: no
Symfony2 tests pass: yes

I was seeing this error in my logs when using an `AppCache`:

```
Error 2: /var/www/beta.example.com/shared/vendor/symfony/symfony/src/Symfony/Component/HttpKernel/HttpCache/Store.php line 92: unlink(/var/www/beta.example.com/releases/20120827020525/app/cache/beta/http_cache/md/c2/88/66a911b5266a57bdd55131a47895b8861dfd.lck): No such file or directory
```

It was only occurring when the `http_cache` file was being primed (i.e. first load).

I've added a simple check to ensure that the file is a valid file before trying to unlink. I also added a missing `@return` docblock. Note: I've chosen to return `false` if the file does not exist as this seems to be the behaviour of the `purge` method.

---------------------------------------------------------------------------

by jonathaningram at 2012-08-29T06:46:52Z

@henrikbjorn done and rebased. Thanks.

---------------------------------------------------------------------------

by jonathaningram at 2012-09-17T22:38:47Z

@henrikbjorn any news on this one? It's currently not possible to use the HTTP Cache without the first request failing.

---------------------------------------------------------------------------

by jonathaningram at 2012-09-25T01:28:38Z

ping @fabpot sorry to keep pushing this, but any chance you could take a look at this?
updated VERSION for 2.1.3
bumped Symfony version to 2.1.4-DEV
Fix export-ignore on Windows
Merge branch '2.0' into 2.1

* 2.0:
  [Form] Fixed NumberToLocalizedStringTransformer to accept both comma and dot as decimal separator, if possible
  Show correct class name InputArgument in error message
  shows correct class name InputOption in error message
  The exception message should say which field is not mapped
  [HttpFoundation] Fix name sanitization after perfoming move
  Add check to Store::unlock to ensure file exists

Conflicts:
	src/Symfony/Bridge/Doctrine/Validator/Constraints/UniqueEntityValidator.php
	src/Symfony/Component/HttpFoundation/File/UploadedFile.php
	tests/Symfony/Tests/Component/Console/Input/InputArgumentTest.php
	tests/Symfony/Tests/Component/Console/Input/InputOptionTest.php
	tests/Symfony/Tests/Component/Form/Extension/Core/DataTransformer/NumberToLocalizedStringTransformerTest.php
	tests/Symfony/Tests/Component/HttpFoundation/File/FileTest.php
	tests/Symfony/Tests/Component/HttpKernel/HttpCache/StoreTest.php
added missing tests from previous merge
merged branch gajdaw/gitattributes-windows (PR #5938)

This PR was merged into the 2.1 branch.

Commits
-------

646a714 Fix export-ignore on Windows

Discussion
----------

Fix export-ignore on Windows

Rules:

    Tests/ export-ignore

don't work on Windows. My proposition is:

    /Tests export-ignore
[HttpKernel] fixed Client when using StreamedResponses (closes #5370)
[HttpKernel] fix typo
Merge branch '2.1'

* 2.1: (24 commits)
  forced Travis to use source to workaround their not-up-to-date Composer on PHP 5.3.3
  [Routing] removed irrelevant string cast in Route
  Fixed typo
  Make YamlFileLoader and XmlFileLoader file loading extensible
  [HttpKernel] fix typo
  Fixed singularization of "prices"
  [Form] Removed an exception that prevented valid formats from being passed, e.g. "h" for the hour, "L" for the month etc.
  [HttpKernel] fixed Client when using StreamedResponses (closes #5370)
  fixed PDO session handler for Oracle (closes #5829)
  [HttpFoundation] fixed PDO session handler for Oracle (closes #5829)
  [Locale] removed a check that is done too early (and it is done twice anyways)
  Update src/Symfony/Component/Validator/Resources/translations/validators.fa.xlf
  Adding new localized strings for farsi validation.
  [HttpFoundation] moved the HTTP protocol check from StreamedResponse to Response (closes #5937)
  [Form] Fixed forms not to be marked invalid if their children are already marked invalid
  [Form] Excluded some tests in NumberToLocalizedStringTransformerTest which fail on ICU 4.4, but work on ICU 4.8
  added missing tests from previous merge
  [Form] Fixed NumberToLocalizedStringTransformer to accept both comma and dot as decimal separator, if possible
  Fix export-ignore on Windows
  Show correct class name InputArgument in error message
  ...

Conflicts:
	.travis.yml
	src/Symfony/Component/Form/Extension/Core/DataTransformer/NumberToLocalizedStringTransformer.php