[HttpKernel] Prevent setting something into frozen container.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | no
| License       | MIT
| Doc PR        | no3

I have a problem with profiler. Symfony tries set `request` into already frozen container. 
Here is my question on mailing list (with full error message): https://groups.google.com/forum/?fromgroups=#!topic/symfony2/UyqdwD7BAh0