Signed-off-by: Adam Vandenberg <flangy@gmail.com>
This issue manifests itself on 10.6 w/ LLVM, and gd may compile
fine on other configurations wihtout it.
Jpeg is a recommended dependency for this software anyway, though,
so add the dep.
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.
