Implemented a bunch of openat flags this morning: RDONLY/WRONLY/RDWR is now enforced, and O_DIRECTORY, O_APPEND, O_TRUNC, and O_EXCL are now supported
I chose to diverge from POSIX on O_DIRECTORY because I think it's kind of lame, but I could change my mind if this comes back to bite me when I start porting real-world software