Add check to Store::unlock to ensure file exists

Fix indentation and shorten code
Add to DateFormats 'D M d H:i:s Y T' (closes #5830)

DateFormat seen on the web
updated vendors for 2.0.18
updated CHANGELOG for 2.0.18
update CONTRIBUTORS for 2.0.18
updated VERSION for 2.0.18
bumped Symfony version to 2.0.19-DEV
[ClassLoader] fixed unbracketed namespaces (closes #5747)
merged branch jonathaningram/issue_5375 (PR #5376)

This PR was merged into the 2.0 branch.

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

Discussion
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[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.

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

@henrikbjorn done and rebased. Thanks.

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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.

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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?
[HttpFoundation] Fix name sanitization after perfoming move
merged branch helios-ag/patch (PR #5496)

This PR was squashed before being merged into the 2.0 branch (closes #5496).

Commits
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9872d26 [HttpFoundation] Fix name sanitization after perfoming move

Discussion
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[HttpFoundation] Fix name sanitization after perfoming move

Bug fix: yes
Feature addition: no
Backwards compatibility break: no
Symfony2 tests pass: yes
Fixes the following tickets: #2577
License of the code: MIT

Further work on #2577, fixes name sanitization, after moving file name with new name with non latin characters in the beginning.

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by stloyd at 2012-09-12T09:52:05Z

You must revert chmod changes.

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by helios-ag at 2012-09-12T14:30:36Z

@stloyd fixed

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by stof at 2012-10-13T21:12:43Z

@fabpot what is the status of this PR ?
The exception message should say which field is not mapped
merged branch mvrhov/patch-2 (PR #5857)

This PR was merged into the 2.0 branch.

Commits
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6b42c8c The exception message should say which field is not mapped

Discussion
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The exception message should tell which field is not mapped