fix(router): respond to hashchange events

Previously if the URL changed in `HashLocation` mode, the router would not pick up the change.
This adds a listener in `HashLocationStrategy` for `hashchange` events to fix the problem.

Closes #5013

modules/angular2/src/router/path_location_strategy.ts

@@ -63,6 +63,7 @@ export class PathLocationStrategy extends LocationStrategy {
 
   onPopState(fn: EventListener): void {
     DOM.getGlobalEventTarget('window').addEventListener('popstate', fn, false);
+    DOM.getGlobalEventTarget('window').addEventListener('hashchange', fn, false);
   }
 
   getBaseHref(): string { return this._baseHref; }