Large refactor to Formula, mostly improving reliability and error handling but
also layout and readability.
General improvements so testing can be more complete.
Patches are automatically downloaded and applied for Formula that return a
list of urls from Formula::patches.
Split out the brew command logic to facilitate testing.
Facility from Adam Vandenberg to allow selective cleaning of files, added
because Python doesn't work when stripped.
Moved Forumla and Cellar/homebrew into Library.
This way the homebrew core files are more sensibly placed, Cellar is
more internally consistent and only generated. And Homebrew is ready for
use straight out of the tarball.
