bind9 doesn't close extra fds

[Paul Vixie]

> > bind8 loops for over a minute on modern hardware for which
> > _SC_OPEN_MAX is often 16777216.
> 
> That *is* quite large...

it sure surprised the heck out of *us*.

> > the bind9 behaviour was minimalistic.
> 
> But is it right?   In my experience, programs are expected to close 
> unnecessary file descriptors when they daemonize.  Perhaps this 
> behavior could be made conditional for the "modern hardware" you 
> mentioned.

we could keep closing until fd>_SC_OPEN_MAX or the number of failed
closes due to EBADF exceeded some threshold (42 being my favourite.)