Fixes #17165: during a scroll animation, touchstart should not trigger the selection of the item

When list items are in a ScrollableView, I don't see any good reason that touching the view during the scroll animation triggers the selection of the item. That is, in addition to solving the problem in #17615 (wrong item being selected in some browsers), avoiding the selection also has the benefit to avoid an unintentional selection. 

Tested on various Android, iOS, BB and WP8 devices without noticing any kind of regression (no perceived slowdown, for instance). 
 
Fixes [#17165](https://bugs.dojotoolkit.org/ticket/17165).