assert: introduce `deepStrictEqual`

`deepStrictEqual` works the same way as `strictEqual`, but
uses `===` to compare primitives and requires prototypes of
equal objects to be the same object.

Fixes: https://github.com/joyent/node/issues/7161
Fixes: https://github.com/iojs/io.js/issues/620
PR-URL: https://github.com/iojs/io.js/pull/639


Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-by: Rod Vagg <rod@vagg.org>