Ticket #2162 (new feature)

Description

Using OpenLayers-2.7 on a touchscreen interface exacerbates the problem of click vs drag. Frequently a users finger rolls a few pixels when they're trying to click on a feature and it ends up as a drag event instead of a click event.

I added a pixelTolerance field (as in the Click.js handler) to the Drag handler so these click events could be propagated while allowing some slop in the click. Attached is a -p0 patch that does this (essentially a copy/paste of the Click handler's code for the same).