Enables you to use base-username instead of domain name for vmailmgrd (and
everything that uses it, like vmailmgr-cgi, omail-admin, etc). Domain naime
is still supported, of course, but this patch allows users which do not have
their own /var/qmail/control/virtdomain entry to admin their emails (which
all look like user-subuser@isp.com, of course, instead of nice
user@virtdomain.com).