OS X now builds without warnings on HEAD

My girlfriend flew back to Vancouver today for summer school. My loss of a girlfriend physically nearby is Python's gain of a developer with time on his hands.

I finally committed the configure.in change so that ``%zd`` support in printf() can be detected. That gets rid of warnings about PY_FORMAT_SIZE_T.

Probably going to do some SoC stuff tomorrow at work. Also planning to work on infrastructure committee stuff next in my spare time.