Also make it build a dylib, not a static library. This is because the default linker behaviour is to run through the search path twice. First time looking for dylibs and second time for .a files. So duplicate formula must build a dylib.
The other option is the -search_paths_first link flag. I don't like this though as every flag we bung in there adds more possible compile issues to projects that depend on such flags being off.
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.
