buffer: throw when writing beyond buffer

Previously one could write anywhere in a buffer pool if they accidently
got their offset wrong. Mainly because the cc level checks only test
against the parent slow buffer and not against the js object properties.
So now we check to make sure values won't go beyond bounds without
letting the dev know.
timers: internal unref'd timer for api timeouts

When an internal api needs a timeout, they should use
timers._unrefActive since that won't hold the loop open. This solves
the problem where you might have unref'd the socket handle but the
timeout for the socket was still active.
net: use timers._unrefActive for internal timeouts
configure: respect the --dest-os flag consistently

Consider a user on his Mac, who wants to cross-compile for his Linux ARM device:

    ./configure --dest-cpu=arm --dest-os=linux

Before this patch, for example, DTrace probes would incorrectly attempt to be
enabled because the configure script is running on a MacOS machine, even though
we're trying to compile a binary for `linux`.

With this patch, the `--dest-os` flag is respected throughout the configure
script, thus leaving DTrace probes disabled in this cross-compiling scenario.
doc: the build requires gcc 4.2 or newer
http: save roundtrips, convert buffers to strings

This commit adds an optimization to the HTTP client that makes it
possible to:

* Pack the headers and the first chunk of the request body into a
  single write().

* Pack the chunk header and the chunk itself into a single write().

Because only one write() system call is issued instead of several,
the chances of data ending up in a single TCP packet are phenomenally
higher: the benchmark with `type=buf size=32` jumps from 50 req/s to
7,500 req/s, a 150-fold increase.

This commit removes the check from e4b716ef that pushes binary encoded
strings into the slow path. The commit log mentions that:

    We were assuming that any string can be concatenated safely to
    CRLF.  However, for hex, base64, or binary encoded writes, this
    is not the case, and results in sending the incorrect response.

For hex and base64 strings that's certainly true but binary strings
are 'das Ding an sich': string.length is the same before and after
decoding.

Fixes #5528.
v8: update to 3.14.5.9
v8: fix GetLocalizedMessage usage

As is the backport of the abort on uncaught exception wouldn't compile
because we it was passing in `this` when it was unnecessary.
v8: re-apply floating patches
http: Return true on empty writes, not false

Otherwise, writing an empty string causes the whole program to grind to
a halt when piping data into http messages.

This wasn't as much of a problem (though it WAS a bug) in 0.8 and
before, because our hyperactive 'drain' behavior would mean that some
*previous* write() would probably have a pending drain event, and cause
things to start moving again.
buffer: special case empty string writes

Prior to 119354f we specifically handled passing a zero length string
to write on a buffer, restore that functionality.
remove bodyHead argument to http 'upgrade' event

streams2 makes this unnecessary
remove bodyHead argument to http 'upgrade' event from documentation
fix tests for HTTP UPGRADE/CONNECT