Tentative fix for the apparent currentURL bug

It turns out that this isn't so much a problem with currentURL as it is
the visit helper. When the lazy router location work was completed in
8e130e5 the call to `router.location.setURL()` was moved down in the
else case after checking for readiness deferrals. The problem seems to be
a timing issue with the call to setupRouter after the application is
marked ready. The initialURL, while set, doesn't give us a reliable URL
during tests.

The fix suggested here is based on my limited understanding of the
lifecycle of the router during boot time. This passes the newly added
url helper tests as well as the existing tests in the test suite.

If it isn't 'the fix' perhaps it can point a way to the real deal.

packages/ember-testing/lib/helpers.js

@@ -57,6 +57,8 @@ function focus(el) {
 
 function visit(app, url) {
   var router = app.__container__.lookup('router:main');
+  router._setupLocation();
+  router.location.setURL(url);
 
   if (app._readinessDeferrals > 0) {
     router['initialURL'] = url;