All POSIX libc api now there (to P1003.1c/D10)
(more md stuff is needed for other libc/arch/*)
(setlogin is no longer a special syscall)
Add -pthread option to gcc (that makes it use -lc_r and -D_POSIX_THREADS).
Doc some re-entrant routines
Add libc_r to intro(3)
dig() uses some libc srcs and an extra -I was needed there.
Add more md stuff to libc_r.
Update includes for the pthreads api
Update libc_r TODO

entire trees for testing anyway, I might as well do this intrusive touching
of include files now.  Added openBSD tags.

Correct _POSIX_ARG_MAX; it should define the minimum allowed argument size,
not the supported on (we have sysconf for that)