rightClick = function (selector, xoffset, yoffset) {
    return handleMouseButtonCommand.call(this, selector, 'right', xoffset, yoffset)
}
Apply right click on an element. If selector is not provided, click on the last
moved-to location.

@alias browser.rightClick
@param {String} selector element to click on
@param {Number} xoffset  X offset to move to, relative to the top-left corner of the element.
@param {Number} yoffset  Y offset to move to, relative to the top-left corner of the element.
@uses protocol/element, protocol/buttonPress
@type action