Patch for router

Let's authenticate on the right req.originalUrl if possible.
res.status().json() seems to work with express 3.x, It is the reason why I am now testing for both express 3x and express 4x here: https://github.com/mozilla-services/express-hawkauth/pull/1/files#diff-354f30a63fb0907d4ad57269548329e3R6

But maybe we should add a specific test for it.