router: Set RemoteAddr in backend request object. Closes #105.

I've added a line to the `http.go` file that sets the RemoteAddr from the `conn` object before passing it on to the handle() function.

I also added tests to verify (from the backend app's point of view) that it is receiving the X-Forwarded-* headers as well as the `X-Request-Start` header.
Is there a reason to do the "initial sync" style initialization in this test? Take a look at the next test for an example of using the helpers.