Fixes to HistoryLocation

This PR fixes several issues with `Ember.HistoryLocation`:

1. `rootURL` was not handled correctly when page loads without the `rootURL` ( i.e. when the URL == '/' ).
2. In one rare case it was not handling `history#popstate` correctly for non-webkit browsers.
3. `history#popstate` fired on page load in webkit browsers when the index route contained a redirect.

This should fix all of the above issues.  It should also fix #2451