Commits
-------

51596d47 Fixed a bug when using http authentication on the security service provider

Discussion
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Fixed a bug when using http authentication on the security service provider

Hi Fabien,

When I added HTTP authentication to my Silex application an exception was thrown. Due the exception I wasn't able to use HTTP authentication when I accessed the application through the browser.

I used the following security firewall:
```php
'http-auth' => array(
    'pattern' => '^.*$',
    'http' => true,
    'users' => array(
        // password is foo
        'admin'  => array('ROLE_ADMIN', '5FZ2Z8QIkA7UTZ4BYkoC+GsReLf569mSKDsfods6LYQ8t+a8EW9oaircfMpmaLbPBh4FOBiiFyLfuZmTSUwzZg=='),
    ),
)
```

The following exception was thrown:
```
InvalidArgumentException: Identifier "security.entry_point.http" is not defined
```

It's a small fix and I also added some tests. All tests passed before I committed my changes.

I would appreciate it when you take a look at this pull request.