koajs/koa — pull request #265 by dead-horse (2014-04-24 17:18:57+00:00)
Title: Throw not error

well, i just write some stupid code:

```js
function exists(file) {
return function (done) {
fs.exists(file, done);
}
}
```

forget `fs.exists` is messed, then the server crashed.

not sure this change make sence, but i think we should take care of it, or it will crash the server.