Re: (ITS#7363) libmdb should use POSIX semaphores on non-apple BSD systems too.

[h . b . furuseth]

I've cleaned up preprocessor names, and remove semaphores more
thoroughly - at init, and after ITS#7377 at at exit failure.

Anything else - like SysV semaphores - can wait until
someone shows up who cares about it.

-- 
Hallvard