Amend the way we handle ACLs to use newer core facilities.

Split uses of admit into admit_ips and admit_hostnames; split def.acl into def.acl_ips and def.acl_hostnames in support of that (but retain def.acl for backwards compability).  Use the escaped version of our domain in the default hostname list; this list is used as regex, so the dots in it are wildcards unless escaped !
Depends on some core changes that actually make admit_ips and admit_hostnames work properly with classic protocol (which previously only knew about admit).
Does the presense of admit_hostnames cause reverse lookups even if the list is empty?