DO NOT MERGE  Silence compile warnings

This branch silences compile warnings, which are getting really out of hand with gcc-4.8.  A fringe benefit is we'll start to notice some of the bugs creeping in with new warnings.

This is NOT READY TO MERGE.  Even once the branch passes the buildbot, it'll need a bunch of eyeballs before I feel good about merging it.

Unfortunately, since the UB RTAPI contract has been diluted steadily since its first release, some warnings remaining in the `xenomai-kernel` threads build will be non-trivial to fix.