Because we modified the ENV global each install this propagated to consecutive
formulae. So exec a new brew process each install. This is the safest way
although Ruby exceptions don't propagate to the parent process so I worry
about it somewhat.
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.
