INTERACTION view hint ever growing on pinch zoom

On Android 4 (Chrome), when pinch zooming on a map, I would expect the `ol.ViewHint.INTERACTING` hint to be `0` after the interaction. But what happens is that it is ever growing the more I interact. Looking at the code, and also with my strange findings from earlier today (#811), I suspect that something is wrong with our touch event system - it looks like not every touchstart has a matching touchend. Do we stopPropagation on touchstart somewhere?