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.
Signed-off-by: Max Howell <max@methylblue.com>
I squashed a number of commits here, and also replaced the use of nspr.prefix with HOMEBREW_PREFIX as in theory we are flexible with our requirement for dependencies, although with the limited build system that SpiderMonkey possesses this is difficult for us to achieve anyway…
