build: reduce tarball size by 8-10%

Slim the tarballs further by removing examples, documentation and test for
third party libraries. Also switch to checkout-index versus archive so we avoid
using tar.

PR-URL: https://github.com/iojs/io.js/pull/961


Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Rod Vagg <rod@vagg.org>