Added skip_rbl_hosts (wildcard domains for reverse IP lookups) and skip_rbl_hosts_ip (IPs and ranges) to be skipped for RBL checks (related to skip_domain_domains for recipient domain)
Related files
/etc/virtual/skip_rbl_hosts (wildlsearch)
/etc/virtual/skip_rbl_hosts_ip (ip or ip/mask)

The changes allow for the files to be missing, as an "if exists" check is done when the lists are loaded.

As the names suggest, this will allow you to fully enable the use_rbl_domains linked to the domains file (enable Admin Settings -> RBL checks),
but will allow you to also skip the checks on major mail networks that your trust.