Add prevent ghostclick functionality.

Adds option to prevent ghost click functionality, on an opt-in basis.

Fixes a multiple click event bug on default browser in Android Jelly Bean 4.1.
See: https://github.com/cubiq/iscroll/issues/270

Also see: https://github.com/cubiq/iscroll/issues/203

Similiar to: https://github.com/cubiq/iscroll/pull/263
but prevents clicks on document.body in addition to clicks on the same iScroll element.