brewkit.rb changes ENV destructively, so lets not do that everytime a formula
is required. Now it's possible for other tools to require a formula
description without worrying about side-effects.
tmux is a "terminal multiplexer", it enables a number of terminals
(or windows) to be accessed and controlled from a single terminal. tmux is
intended to be a simple, modern, BSD-licensed alternative to
programs such as GNU screen.
