http: optimize outgoing requests

This commit does some small optimization changes on
`lib/_http_outgoing.js`. These include switching from `while` loops to
`for` loops, moving away from `util` to `typeof` checks, and removing
dead code. It also includes variable caches to avoid lookups and
generic style changes. All in all, much faster execution.

It gets an across the board increase in req/sec on the benchmarks,
from my experience about a 10% increase.

PR-URL: https://github.com/iojs/io.js/pull/605


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Nicu Micleușanu <micnic90@gmail.com>
Reviewed-By: Christian Vaagland Tellnes <christian@tellnes.com>
Reviewed-By: Brian White <mscdex@mscdex.net>