async_wrap: notify post if intercepted exception

The second argument of the post callback is a boolean indicating whether
the callback threw and was intercepted by uncaughtException or a domain.

Currently node::MakeCallback has no way of retrieving a uid for the
object. This is coming in a future patch.

PR-URL: https://github.com/nodejs/node/pull/5756


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Andreas Madsen <amwebdk@gmail.com>