loadCallback = function () {
				this.removeEventListener('load', loadCallback, false);
				this.removeEventListener('error', errorCallback, false);

				cc.loader.cache[url] = img;
				if (callback)
					callback(null, img);
			}
Load a single image.
@param {!string} url
@param {object} [option]
@param {function} callback
@returns {Image}