Function when

test/curl.js:180–189

(promiseOrValue, callback, errback, progback)

	}

	function when (promiseOrValue, callback, errback, progback) {
		// we can't just sniff for then(). if we do, resources that have a
		// then() method will make dependencies wait!
		if (isPromise(promiseOrValue)) {
			return promiseOrValue.then(callback, errback, progback);
		}
		else {
			return callback(promiseOrValue);
		}
	}

	/**
	 * Returns a function that when executed, executes a lambda function,