Resolve clang scan-build issues
The clang analyzer tool "scan-build" reports a bunch of issues on current Tor master. On inspection, I believe that there's nothing harmful here. (Stuff is false-positive, or harmless, or both.) But we should nevertheless clean it all up if we can.
For extra points, we should integrate "scan-build" as part of our build hygiene process, and get jenkins to flip out when it doesn't pass error-free.