fs: add recursive subdirectory support to fs.watch

Currently fs.watch does not have an option to specify if a directory
should be recursively watched for events across all subdirectories.

Several file watcher APIs support this. FSEvents on OS X > 10.5 is
one example. libuv has added support for FSEvents, but fs.watch had
no way to specify that a recursive watch was required.

fs.watch now has an additional boolean option 'recursive'. When set
to true, and when supported, fs.watch will return notifications for
the entire directory tree hierarchy rooted at the specified path.
tls: reuse hostname from underlying net.Socket

When `tls.connect()` is called with `socket` option, it should try to
reuse hostname previously passed to `net.connect()` and only after that
fall back to `'localhost'`.

fix #6409
tls: do not default to 'localhost' servername
node: add AsyncListener support

AsyncListener is a JS API that works in tandem with the AsyncWrap class
to allow the user to be alerted to key events in the life cycle of an
asynchronous event. The AsyncWrap class has its own MakeCallback
implementation that core will be migrated to use, and uses state sharing
techniques to allow quicker communication between JS and C++ whether the
async event callbacks need to be called.
async-wrap: integrate with WeakObject

Making WeakObject inherit from AsyncWrap allows us to peak into almost
all the MakeCallback calls in Node internals.
async-wrap: add methods to udp/tcp/pipe/timers

Now it's possible to add/remove an async listener to an individual
handle created by UDP, TCP, Pipe or Timer.
crypto: convert RandomBytesRequest to a class

Since RandomBytesRequest makes a call to MakeCallback, needed it to be
a class so AsyncWrap could handle any async listeners.

Also added a simple test for an issue had during implementation where
the memory was being released and returned.
crypto: convert pbkdf2_req to a class

pbkdf2_req has been renamed to PBKDF2Request and converted to a class.
It now uses AsyncWrap::MakeCallback.

Also includes, using env()->ondone_string() instead of "ondone" and
using malloc instead of new char[].
cares: add AsyncListener support
domain: use AsyncListener API

The domain module has been switched over to use the domain module API as
much as currently possible. There are still some hooks in the
EventEmitter, but hopefully we can remove those in the future.
test: add additional async listener tests
doc: add docs for AsyncListeners

Documentation has been added on how to use the AsyncListener API.