Cleanup

Sorry, that's a one massive commit since I touched many things while trying to make it work here. At least it has a thorough description ;-).

Questions: 
- This doesn't index Keychain Items, only Keychains. I was thinking to change that, but it's debatable.
- This creates objects for *everything* in the keychain, including things like Certificates, Identities and Keys, which are basically useless since I can't find useful actions for.
- @HenningJ: Can you check how that goes on 10.6 ? There are parts that aren't available there, and I want to know how much of it is usable there. As far as I can tell, 10.6's `SecItemCopyMatching` is limited to Internet Passwords only, and I'm afraid this will degenerate in a Keychain-wrapper-creation-frenzy if this is true.