readdir_r is not POSIX according to POSIX_SOURCE, bruce says:
> readdir_r() is in the _POSIX_SOURCE section, but is not a POSIX.1-1990
> function. It's POSIX.1-1996 so it should be under a different feature
> test which we don't support yet.
make sure errno is saved so that its contents are cleared unless
necessary.
Submitted by: bde
eischen (Daniel Eischen) added wrappers to protect against cancled
threads orphaning internal resources.
the cancelability code is still a bit fuzzy but works for test
programs of my own, OpenBSD's and some examples from ORA's books.
add readdir_r to both libc and libc_r
add some 'const' attributes to function parameters
Reviewed by: eischen, jasone
