Fix #241. Ignore virtual path prefix of request URL when checking route.

Ignore virtual path prefix of request URL when performing optimized checking of static left part of route.

Enables a virtual path to be used after the port for self-hosted WebAPI so that multiple apps can bind to the same port. e.g.

`var config = new HttpSelfHostConfiguration("http://localhost:8080/root")`

Previously, the virtual path was ignored when performing the short-circuit check of the request URL against the route which meant routes that should have matched didn't and returned 404.