- switch to the NetBSD identifier system; it is not only better, but
also required for porting NetBSD ipcs(1) and ipcrm(1); however, it
requires that slots not be moved, and that results in some changes;
- synchronize some other things with NetBSD: where keys are kept, as
well as various non-permission mode flags;
- fix semctl(2) vararg retrieval and message field type;
- use SUSPEND instead of weird reply exceptions in the call table;
- fix several memory leaks and at least one missing permission check;
- improve the atomicity of semop(2) by a small amount, even though
its atomicity is still broken at a fundamental level;
- use the new cheaper way to retrieve the current time;
- resolve all level-5 LLVM warnings.