Speedup closing of fds before exec.
Speedup closing of fds before exec.

* src/posix-io.c [__linux__]: Include dirent.h.
(get_max_fds) [__linux__]: Try to figure out the highest used fd.
--

Signed-off-by: Werner Koch <13bd1fc5137f503b0a8355ad400e7a87ebb45b25@gnupg.org>

gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme