Speedup closing fds before an exec.
* src/system-posix.c [__linux__]: Include dirent.h. (get_max_fds) [__linux__]: Return the actual used highest fd.
This is the same code as introduced with the
GnuPG commit 512c56af43027149e8beacf259746b8d7bf9b1a2
- Signed-off-by: Werner Koch <wk@gnupg.org>