make-secnet-sites: Tolerate late `complain'

make-secnet-sites: Tolerate late `complain'

In e5baf0cd0e91353194df02c4c376b0c472f49ec2
  make-secnet-sites: Crash if complain() is called too late
we checked for this.

But actually we want to support it.  Do so by exiting right away.

So, early enough complaints are saved up.  Late ones cause immediate
exit.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>