When you call 'request.params' in a constraint matcher, subsequent
routes don't have their path attributes set correctly.
In this case, a URL of '/about' would have params[:something] == 'about' in the route
Adding this constraint and route causes the following test to fail.
<"home"> expected but was
… subsequent routes. [Closes #2510]
As the same request is reused thru all the routing constraints,
accessing a memoized form of `params` would prevent the router from
redefining it with a new set of parameters (the current route