src: redo unaligned access workaround

Introduce two-byte overloads of node::Encode() and StringBytes::Encode()
that ensure that the input is suitably aligned.

Revisits commit 535fec8 from yesterday.
src: move BE/LE buffer conversion to StringSlice()

Move the big endian to little endian conversion logic for UCS2 input
from src/string_bytes.cc to src/node_buffer.cc; StringSlice() is the
only function that actually needs it and with this commit, a second
copy is avoided on big endian architectures.
lib: reintroduce v8 module

I introduced this module over a year ago in a pull request as the v8
module but it was quickly subsumed by the tracing module.

The tracing module was recently removed again and that is why this
commit introduces the v8 module again, including the new features it
picked up commits d23ac0e and f8076c4.

PR-URL: https://github.com/iojs/io.js/pull/131
Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>
Reviewed-By: Christian Tellnes <christian@tellnes.no>
Reviewed-By: Thorsten Lorenz <thlorenz@gmx.de>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>