fix start routine to not rely on controller.location...

see Issue #893.

Instead, we'll keep the prev location stored in the start function and
compare the new location to the previous location that way. Thanks to
@saimeunt for pointing out the mistake and offering a suggested fix.

Also, invalidate the getParams computations if hash changes, when we do
the scroll to hash routine in the start function of router_client.js.
Merge branch 'devel' of github.com:EventedMind/iron-router into devel