Do not load the hash as a fallback.

While doing some debugging for #2566, I ran across this [line of code][code].  It appears to contain a fallback so that an unsuccessful execution of `loadUrl` (matching no routes) will attempt to load the hash instead.  I'm not certain why this was originally added, though I suspect it concerns Firefox hash bugs.

All the tests pass without the fallback and it fixes the subtle bug described by the attached test case.

[code]: https://github.com/braddunbar/backbone/blob/61987e8debca6a80b5ac07eef8a0d774a150cda2/backbone.js#L1444