Resolve the normalized route at the end of the request

[dividedmind]

We currently try to resolve the normalized route when the request comes in instead of when it's finished. In some environments this can be problematic; eg. devise provides route constraints that rely on certain request environment fields being filled by a middleware that only runs late in the stack (cf. issue #358).

If we move the normalized route resolution to the request finalizer we can be reasonably certain that all prerequisites are met.