Paging: Remove double drag stuttering

[pbakaus]

When paging is activated, and you drag from one page to another and then drag again while the deceleration of the first page change isn't completed, Scroller immediately "jumps" to the next page before taking the next drag.

The native paging controls Apple do not work this way, so it probably makes sense to consider this a bug.

[swernerx]

Sounds like something we should have a look at.

[drkibitz]

The proper way to do this is to simply stop deceleration if it is currently decelerating, and immediately beginning a drag scroll. Essentially, if we are decelerating doTouchStart should actually behave like doTouchMove.

To give us more fine grain control, which I would like is simply adding a public property of "isDecelerating". This is an example of simple logic where people would be fine to do themselves if it was part of the public API.