BUG/MEDIUM: make RGroups working in mode stat, not only config mode

Also copy the Rgroups from parent to child when merging configurations.

That kind of configuration was broken :

  <VirtualHost *:80>
    DocumentRoot /var/www/localhost/htdocs

    RMode stat
    RGroups nogroup
    RMinUidGid     #1000  #1000
    RDefaultUidGid apache apache
  </VirtualHost>
BUG/MINOR: Add all RGroups, even when when group is not matching MIN_GID