Improve scrolling cache (ported from ICS)

Scrolling cache helps make short scrolls/flings smooth but will
cause stutter when long flings are made. This patch automatically
disables scrolling cache when long flings are made.

ported from ICS commit, http://review.cyanogenmod.com/#change,12537

Change-Id: I120a5ac50b36dfcdab16ef77aed5ac40930a2dc5