Don't emit the 'close' event with process.nextTick.
Closing a handle is an operation that usually *but not always* completes
on the next tick of the event loop, hence using process.nextTick is not
reliable.
Use a proper handle close callback and emit the 'close' event from
inside the callback.
Update tests that depend on the intricacies of the old model.
Fixes#3459.
Said test relies a great deal on internals and implementation details (I should
know, I wrote it). Patch it up to work with libuv's new refcounting scheme.
* process._getActiveHandles() returns a list containing all active handles
(timers, sockets, etc.) that have not been unref'd.
* process._getActiveRequests() returns a list of active requests (in-flight
actions like connecting to a remote host, writing data to a socket, etc.).