Fix xml route configuration for routing condition

Current XML documentation doesn't respect routing schema (https://github.com/symfony/symfony/blob/master/src/Symfony/Component/Routing/Loader/schema/routing/routing-1.0.xsd)
bug #4012 Fix xml route configuration for routing condition (xavierbriand)

This PR was submitted for the master branch but it was merged into the 2.4 branch instead (closes #4012).

Discussion
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Fix xml route configuration for routing condition

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.4+
| Fixed tickets |  #4011

Commits
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6790fb2 Fix xml route configuration for routing condition