[BrowserKit] Fix #10641 : BrowserKit is broken when using ip as host
bug #10649 [BrowserKit] Fix #10641 : BrowserKit is broken when using ip as host (romainneutron)

This PR was merged into the 2.3 branch.

Discussion
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[BrowserKit] Fix #10641 : BrowserKit is broken when using ip as host

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #10641
| License       | MIT

As documented in http://php.net/manual/en/function.preg-replace.php, we have to use the `$` notation for replacing the backreference

>When working with a replacement pattern where a backreference is immediately followed by another number (i.e.: placing a literal number immediately after a matched pattern), you cannot use the familiar \\1 notation for your backreference. \\11, for example, would confuse preg_replace() since it does not know whether you want the \\1 backreference followed by a literal 1, or the \\11 backreference followed by nothing. In this case the solution is to use \${1}1. This creates an isolated $1 backreference, leaving the 1 as a literal.

Commits
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e946da3 [BrowserKit] Fix #10641 : BrowserKit is broken when using ip as host