Handle old host-regex properly as sub-domain in new ACL.

This resolves
     TODO clean up possible regex, if it starts with ".*"
     then store two entries: entry, and *dot*entry.
from an old comment.  I'd inadvertently implemented this direction of
mapping by mistake when I set out to do the - much easier (see
previous commit) - reverse transform and got confused.  So, might as
well not waste it.

Note that a regex that doesn't make sense as either a sub-domain match
or a simple domain name shall now be ignored, where it was previously
added to the host-name ACL; but, since it wouldn't have matched
anything anyway in the new-style ACL, there should be no harm in
omitting it.

(cherry picked from commit 08dce3a22d1e5c97adb5f664beb552d2b58886b0)