Only set interacting hint when modifying the view

This PR follows up on https://github.com/openlayers/ol3/pull/1277 by applying the same changes to the touch interaction.

This should also fix a bug in the vector-api branch where vector layers are not redrawn after pinch-zooming. @oterral, you can use my [`vector-api-interaction-hint`](https://github.com/elemoine/ol3/compare/openlayers:vector-api...vector-api-interaction-hint) if you want to test my commit with the vector-api branch.

Please test and review.