stream: Short-circuit buffer pushes when flowing

When a stream is flowing, and not in the middle of a sync read, and
the read buffer currently has a length of 0, we can just emit a 'data'
event rather than push it onto the array, emit 'readable', and then
automatically call read().

As it happens, this is quite a frequent occurrence!  Making this change
brings the HTTP benchmarks back into a good place after the removal of
the .ondata/.onend socket kludge methods.
src: use v8::String::NewFrom*() functions

* Change calls to String::New() and String::NewSymbol() to their
  respective one-byte, two-byte and UTF-8 counterparts.

* Add a FIXED_ONE_BYTE_STRING macro that takes a string literal and
  turns it into a v8::Local<v8::String>.

* Add helper functions that make v8::String::NewFromOneByte() easier to
  work with. Said function expects a `const uint8_t*` but almost every
  call site deals with `const char*` or `const unsigned char*`. Helps
  us avoid doing reinterpret_casts all over the place.

* Code that handles file system paths keeps using UTF-8 for backwards
  compatibility reasons. At least now the use of UTF-8 is explicit.

* Remove v8::String::NewSymbol() entirely. Almost all call sites were
  effectively minor de-optimizations. If you create a string only once,
  there is no point in making it a symbol. If you are create the same
  string repeatedly, it should probably be cached in a persistent
  handle.
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.
build: don't auto-destroy existing configuration

Don't run configure when the configure script has been touched. Doing so
would be okay if the Makefile passed the original arguments to configure
but it doesn't - it runs configure without any arguments, effectively
destroying the current configuration.

Remove this misfeature and instead print an error message telling the
user to (re-)run configure.
 build: make ninja build respect V=

 Compiling with `make V=1` (which is the default) now runs ninja in
 verbose mode. To disable, run `make V=`.
configure: order configure switches alphabetically

Alphabetical order should make it easier to find the switches you need
because we've got quite a lot of them now.

Keep --prefix at the top because that's arguably the one people will be
looking for most.
build: fix up style issues in configure script

* Use single quotes consistently.
* Remove a few stray semicolons.
* Fix up some overly long lines.
* Line up a few expressions.
build: disable SSLv2 by default

No one in this day and age should be using SSLv2 so disable it by
default. You can re-enable it with `./configure --with-sslv2` but
there really should be no reason for that.
v8: upgrade v8 to 3.20.14.1
v8: fix openbsd build

This is [1] applied ahead of time. Summary:

    OpenBSD doesn't have <ucontext.h>. ucontext_t lives in <signal.h>
    and is a typedef for struct sigcontext. There is no uc_mcontext.

[1] https://codereview.chromium.org/21705003/

Note: the patch has been accepted upstream but hasn't made its way into
a stable release yet.
stream_wrap: use v8::Integer::NewFromUnsigned()

Use v8::Integer::NewFromUnsigned() when updating the writeQueueSize
field.

Before this commit, it used v8::Integer::New() but that takes an
int32_t. It's unlikely for a write queue to grow beyond 2**31-1 bytes
but let's use the unsigned integer constructor anyway, just in case.
test: fix up internet/test-dns after api change

* The test calls an internal API that changed in commit ca9eb71.

* Trying to reverse-lookup a bogus hostname now returns EINVAL rather
  than the (bogus!) status code ENOTIMP.
cares_wrap: don't set oncomplete property from c++

Don't set the oncomplete property in src/cares_wrap.cc, we can do it
just as easily in lib/dns.js.

Switch two closures to the 'function with _this_ object' model. Makes
it impossible for an overzealous closure to capture too much context
and accidentally hold on to too much memory.
cares_wrap: remove unused function getHostByName()

Hasn't been used in ages. Also remove its (already disabled) test.