koajs/koa — pull request #173 by vesln (2014-01-04 08:34:57+00:00)
Title: context.throw supports Error instances

This modifies `ctx.throw` so it supports `Error` instances.

before:

```js
if (err) {
err.status = 422;
err.expose = true;
throw err;
}
```

after:

```js
if (err) this.throw(err, 422);
```