Fix build and some lost commits.

This fixes (partly) the build under Xcode 5. The "partly" is due to Sparkle still relying on the 10.7 SDK, which I don't have anymore (Xcode 5 took care of it).

I reworked most `#import`s to be more "standard" (see b8df7e0), and added a few commits I had lying around.

This also depends on https://github.com/andymatuschak/Sparkle/pull/298 for a hard error under Xcode 5.