When unsetting maxBounds, moveend event remains bound and causes errors

If you set the maxBounds for a map, and then decide to remove them, the function does not unregister to moveend event which causes errors and inappropriate scaling.

I made a fiddle which demonstrates the issue: http://jsfiddle.net/jec006/PfJ8m/

I think the proper solution is simply unbinding the moveend event if !bounds and will create a pull request to that effect
