Cancelling any ongoing animation in UIScrollView

If there is any UIScrollView animation of any sort:
- Say the user scrolled a little bit and the UIScrollView is decelerating. 
- Or `[scrollView setContentOffSet:p animated:YES]` was triggered.
- Or the user tapped on the statusbar to scroll to top

These animations will interfere with pop-animation since they will both work simultaneously. Setting `-[UIScrollView setContentOffset:animated:]` will cancel/stop any UIScrollView animation.
Merge pull request #100 from hfossli/patch-1

Cancelling any ongoing UIScrollView animation