Initial touchscreen support. Lots of debugging code and TODOs remaining.
Added an option to control whether touch events can scroll the page by less than the STEP_SIZE. Disabling it may improve compatibility (as the page will then only scroll by the same amounts that keypresses, clicking the scroll bar and moving the mousewheel would do), but leaving it enabled results in smoother, more natural touch-scrolling.
Fixed up the touch-scroll behaviour for when step-size is enforced for touch-scrolling.
Implemented a new "touchDistanceAmplificationFactor" option which allows the touch move distance to be amplified by a set amount so that the page scrolls that much faster than the user moves their finger (or other touch device).
Should now better handle multiple touches
Tidied up the touch-support code and added some more comments.
Merge branch 'touch-support'

Conflicts:
	script/jquery.scrollpath.js