dragging on right click ( reopened ticket 6909 )

I reopened this ticket http://bugs.jqueryui.com/ticket/6909

Using the "which" option to target a specific mouse button. like in this example http://threedubmedia.com/code/event/drag/demo/which

$(myDIv).draggable({distance: 5, zIndex: 2700,which:3});

it is related to this jquery.ui.mouse.js

_mouseDown: function(event) {
		// don't let more than one widget handle mouseStart
		// TODO: figure out why we have to use originalEvent
		event.originalEvent = event.originalEvent || {};
		if (event.originalEvent.mouseHandled) { return; }

		// we may have missed mouseup (out of window)
		(this._mouseStarted && this._mouseUp(event));

		this._mouseDownEvent = event;

		var self = this,
			btnIsLeft = (event.which == 1), '''<--- Add support to specify this'''
			elIsCancel = (typeof this.options.cancel == "string" ? $(event.target).parents().add(event.target).filter(this.options.cancel).length : false);
		if (!btnIsLeft || elIsCancel || !this._mouseCapture(event)) {
			return true;
		}