Assorted clean-ups, mostly related to compiler warnings.

[gutschke]

I tried building the firmware myself and ran into a couple warnings and minor issues. Can you take a look. If you want to apply the pull request, that's fine. But you can also just cherry pick individual fixes after confirming they make sense. I was mostly just guessing what might be needed.

Also, no idea why the uart2.cpp file appears to be in DOS encoding. "git diff" shows an ugly ^M that I can't make disappear. Maybe, that's what it is supposed to do in order to warn me, but everything is actually correct?

N.B.: This is the first time ever that I have used the GitHub feature for pull requests. Let me know if I messed things up.