fix glitch in animated scale

[incanus]

Per @kkaefer:

When zooming in, this always moves back to an intermediary state for me, like snapping to integer zoom levels or something.

http://i.kkaefer.com/Movie_on_06.02.14_at_15.53.mov

[incanus]

This was a fun little one. Turns out 61c69f5 introduced the unintended consequence of recognizing the pan, pinch, and/or zoom gestures on either side of a simultaneous resolution comparison with the (animated) two-finger single-tap gesture and allowed the tap end to resolve, too, introducing a small, animated zoom out, i.e., two finger pan/pinch/zoom end would also trigger two-finger tap end.