Add more context when throwing 'Uncaught, unspecified "error" event.'

[binarykitchen]

Could you please add more context when throwing this error at
https://github.com/joyent/node/blob/master/lib/events.js#L89

Because like that, it's not very helpful. Sometimes I get these errors when having lots of async operations without having attached an error listener yet. Without knowing the real error it is trying to emit, it is extremely difficult to improve code.

Suggestion is to change this line:

throw Error('Uncaught, unspecified "error" event.');

into something like this:

throw Error('Uncaught, unspecified "error" event. The initial error it was trying to emit was:', arguments);

[jasnell]

While I think the change is good, I'm not sure it's a priority for either v0.12 or v0.10. We can pick the iojs change up in the converged stream.