Prevent 'tap' event from beeing triggered after scrolling

The tap event is always triggered after scrolling. So the element
which is under the finger after scrolling stops is triggered with a
'tap'. 
With my change the positions of 'touchstart' and 'touched' are compared.
Only if they are within an given threshold of 10 px, 'tap' is executed.

Thanks to Ryan Fioravanti :
http://code.google.com/intl/de-DE/mobile/articles/fast_buttons.html