Raise compat_* testing to over 80%
compat.c.gcov 360 426 54.20
compat_libevent.c.gcov 92 32 25.81
compat_pthreads.c.gcov 22 72 76.60
compat_threads.c.gcov 48 51 51.52
Getting 95% coverage for stuff that relies on OS functionality might not be feasible, but it would be great to get this as high as possible.
(Stubbing OS calls out is probably not the best answer here, even though you might think it would be. We're not only interested in whether our compatibility wrappers do the right thing when the OS behaves the way we expect: we're also interested in whether they do the right thing on the actual OS. )