It seems that the main GNU download site has issues in some places
outside the U.S., so we'll use the provided "ftpmirror.gnu.org" to pick
a nearby mirror.
Signed-off-by: Jack Nagel <jacknagel@gmail.com>
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.