URL is decoded twice.

Hey,
I have the following problem:

    (context "/ip" []
        (GET "/:ip" [ip]
           ip))

I believe that it should match `http://localhost:3000/ip/0%3A0%3A0%3A0%3A0%3A0%3A0%3A1%250`, which is just url encoded `http://localhost:3000/ip/0:0:0:0:0:0:0:1%0` (IPv6 localhost). The error is `URLDecoder: Incomplete trailing escape (%) pattern` so it just tries to decode %0 again.

It might be related to issue #76.

I created a test that shows the problem. First two tests work, the last one fails (throws exception).