The compatibility normalizer previously missed or was overly egregious
in several cases. This commit resolves those issue. In particular:
* Only request URIs that would not match any route are normalized.
* Synthetic routes are added to the igniting `Rocket` so that requests
with URIs of the form `/foo` match routes with URIs of the form
`/foo/<b..>`, as they did prior to the trailing slash overhaul.
Tests are added for all of these cases.
