- Fix retval handling in bin_setopt()
- Don't skip_setuid / skip_setgid. It's not our place to optimize away noops
(that might not even _be_ noops; they might change the saved uid…).
- Remove HAVE_* guard checks around functions that are used unguarded elsewhere.
- Use bsd-setres_id.c from OpenSSH to provide setresuid() / setresgid()
everywhere, and thus simplify the ifdef soup. Fix some preëxisting
bugs in the macro definitions of setuid() (do we still need that one?).
- Fix zwarning() format codes for variadic arguments type safety
- Restored a comment from HEAD
- Fix failure modes around initgroups()
- Compared privilege restoration code with OpenSSH's permanently_drop_uid() and
updated as needed
- Add E01 PRIVILEGED sanity checks
