Add integration tests for Unicode in URL

Apologies if there are already tests for these cases, but I didn't see them.

These test a few cases where a URL contains Unicode characters in it -- a 404 and a 200. Both work fine.

The only thing that doesn't work is that if one calls `str(context)` in the `NotFound` handler, then you get a `UnicodeDecodeError`, but I guess this is reasonable; one should call `unicode(context)` instead I suppose.