Always use Error constructor

[niclashoyer]

While testing the modules I noticed that at some points the errors are not constructed properly. Just passing an object as error is bad, because there is no information on the location (line) and no stack trace. If node the prints the error to the console, the object is converted to string which results in

[object Object]

The change is probably needed in a lot of files, e.g.
add.js line 52:

cb({
    msg : stderror.split('\n')[0],
    cmd : cmd.concat(args).join(' '),
    code: error.code
});

should be

var err = new Error(stderror.split('\n')[0]);
err.cmd = cmd.concat(args).join(' ');
err.code = error.code;
cb(err);

[diosney]

Yeh, you're right, I will change that anytime soon, thanks :)