dgram: fix regression in string argument handling

v0.10 allows strings for the offset, length and port arguments to
dgram.send() and dgram.sendto() but master before this commit would
abort with the following assert:

    node: ../../src/udp_wrap.cc:227: static void
    node::UDPWrap::DoSend(const v8::FunctionCallbackInfo<v8::Value>&,
    int): Assertion `args[2]->IsUint32()' failed.

Go beyond what v0.10 does and also add range checks: offset and length
should be >= 0, port should be between 1 and 65535.

That particular change needs to be back-ported to v0.10 because passing
a negative offset or length number aborts with the following assertions:

    node: ../../src/udp_wrap.cc:264: static v8::Handle<v8::Value>
    node::UDPWrap::DoSend(const v8::Arguments&, int): Assertion
    `offset < Buffer::Length(buffer_obj)' failed.

Or:

    node: ../../src/udp_wrap.cc:265: static v8::Handle<v8::Value>
    node::UDPWrap::DoSend(const v8::Arguments&, int): Assertion
    `length <= Buffer::Length(buffer_obj) - offset' failed.

Interestingly enough, a negative port number is accepted in v0.10 but
is silently ignored.

This commit exposed a bug in the simple/test-dgram-close test which
has also been fixed.
dgram: don't call into js when send cb is omitted

Speed up dgram.Socket#send()-heavy code a little by omitting the call
into JS land when the user doesn't pass us a completion callback.
src: fix windows build breakage from f674b09

The TWO_BYTE_BUFFER macro never made it into the final version of
the patch that got landed in commit f674b09.
test: use common.PORT in simple/test-net-GH-5504
src: don't call v8::Object::SetHiddenValue()

Don't use v8::Object::SetHiddenValue() to keep a reference alive to the
buffer, we can just as easily do that from JS land and it's a lot faster
to boot.

Because the buffer is now a visible property of the write request
object, it's essential that we do *not* log it - we'd be effectively
serializing the whole buffer to a pretty-printed string.
node: remove domain nextTick

It's ridiculously cheap to check if process.domain is set. Don't bother
cluttering the code.
domain: share object and state with native land

Change process.domain to use a getter/setter and access that property
via an array index. These are much faster to get from c++, and it can be
passed to _setupDomainUse and stored as a Persistent<Array>.

InDomain() and GetDomain() as trivial ways to access the domain
information in the native layer. Important because we'll be able to
quickly access if a domain is active. Instead of just whether the domain
module has been loaded.