Function attempt

when.js:121–127

* Call f in a future turn, with the supplied args, and return a promise * for the result. * @param {function} f * @returns {Promise}

(f /*, args... */)

	 * @returns {Promise}
	 */
	function attempt(f /*, args... */) {
		/*jshint validthis:true */
		for(var i=0, l=arguments.length-1, a=new Array(l); i<l; ++i) {
			a[i] = arguments[i+1];
		}
		return apply(f, this, a);
	}

	/**
	 * Creates a {promise, resolver} pair, either or both of which