allow middleware preroute to prevent main route processing

the author of a preroute can return FALSE to indicate the preroute decided the main logic line should NOT be executed.  As an example:

The preroute can decide the user isn't logged in, and forward to the login page, issue a 401 or supply an error JSON.  Processing ahead would require enrichment of the request and the controller to be aware of the enrichment.  I'm too lazy to do that, so instead I'd just like the router to suspend operation at that point.