- Fix semantics: seekdir(pos); telldir() shoud return pos. The code
that implements this will be made faster in a later commit.
- We loose documented behaviour (after closedir() the telldir()
positions are not valid anymore). This was never in Posix, and most
other systems have nothing like it.
Diff originally from Paul Thorn, rewritten by me using some FreeBSD
code.  "slap it in" deraadt@

in sys/cdefs.h) instead of _FOO_SOURCE.  Also fix several namespace
pollution issues, including the byte order defines.  OK deraadt@

ok deraadt@

You must have an up-to-date gcc for this!
deraadt@ ok

rescinded 22 July 1999.  Proofed by myself and Theo.

OK mickey@ and discussed with deraadt@

__null is a magic constant of integral type that converts to a null pointer
as should be, but warns for ambiguity when used to resolved an overload
between an integral type and a pointer type.

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.