[Node] Errno property can either be a number, or a string.

Yes, this is quite strange, but it appears to depend on which library is throwing it.

fs module:
```javascript
$ node
> var fs = require('fs');
undefined
> fs.open('doesntexistlol', 'r', function(e) { console.log(Object.keys(e)); console.log(e.code); console.log(e.errno); console.log(e.path); });
undefined
> [ 'errno', 'code', 'path' ]
ENOENT
34
doesntexistlol
```

dns module: See test https://github.com/joyent/node/blob/v0.10.23-release/test/internet/test-dns.js#L148

As a result, I'm punting to the 'any' type.