bug #22676 [FrameworkBundle] Adding the extension XML (flug)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes #22676).

Discussion
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[FrameworkBundle] Adding the extension XML

| Q             | A
| ------------- | ---
| Branch?       | <3.3
| Bug fix?      | yes
| New feature?  | no <!-- don't forget updating src/**/CHANGELOG.md files -->
| BC breaks?    | no
| Deprecations? | no <!-- don't forget updating UPGRADE-*.md files -->

![XmlUtils](https://cloud.githubusercontent.com/assets/1810304/25841740/9b655036-34a1-11e7-9d1e-a23928b8ed17.png)

This pull request is referenced on ![symfony/skeleton](symfony/skeleton#7)
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Commits
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6fe2ad0 [FrameworkBundle] Adding the extension XML

src/Symfony/Bundle/FrameworkBundle/composer.json

@@ -17,6 +17,7 @@
     ],
     "require": {
         "php": ">=5.3.9",
+        "ext-xml": "*",
         "symfony/asset": "~2.7",
         "symfony/dependency-injection": "^2.6.2",
         "symfony/config": "~2.4",