Consistency between pushState and onpopstate

[chenghaoc]

1. Consistency between pushState and onpopstate, the user registered actions should be called after state changed.
2. Check state path to avoid the problem which will occur when other lib also modify the history state object.

[coveralls]

Coverage decreased (-2.2%) to 87.05% when pulling eb25e04 on changbenny:consistency into aa60550 on visionmedia:master.

[matthewp]

I think this would fix #293. Do you have time to submit a test by any chance?

[matthewp]

Going to close for now, let me know if you have a code example or test you can add.