test: add asyncListener tests

These tests should cover all basic uses of the asyncListener API.
node: add basic asyncListener skeleton

The implementation necessary before other parts of Node can start
calling the asyncListener.
src: add preliminary support for asyncListener

AsyncListener support has been added to ReqWrap, Timers, Events and
nextTick. The listeners will not yet propagate with asynchronous
callbacks called within other callbacks.
src: support for catching nested async callbacks

Async listeners should now propagate through nested callbacks.

Note: This is NOT performance ready. It's simply getting the
functionality to work.
src: fix two syntax errors

First was an improper comparison with bool to int. Second was to "throw
error" instead of "throw new Error".