darcs patch: cabal init

Hi all, I've attached the (long-awaited) patch adding a 'cabal init' command. There's still lots that could be improved but I think it's now at a useful/complete enough state to be released into the wild. Credit also goes to Benedikt Huber who developed a lot of the automagic-guessing heuristic goodness. Naturally, comments/suggestions/improvements welcome! -Brent