Fix duplicate history with same queryParams

Fix https://github.com/emberjs/ember.js/issues/4279

Demo: http://fiddle.jshell.net/indream/GWA8W/5/show/light/
(Click the link twice will produce duplicate history)

This won't happens in application route: http://fiddle.jshell.net/indream/GWA8W/4/show/light/

Fixed Demo: http://fiddle.jshell.net/indream/GWA8W/16/show/light/