Without this change the following error was output for my homebrew location
==> /installer --auto /Users/joel/.homebrew/Cellar/ruby-enterprise-edition/2009.10 --no-tcmalloc -c --enable-shared
invalid option: --auto /Users/joel/.homebrew/Cellar/ruby-enterprise-edition/2009.10
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.