Save domain and GID for groups from the configured domain
    
    Currently users from subdomains can only be members of groups from the
    configured domain and to access those groups a pointer to the domain
    struct of the configured domain is used.  This patch sets the dom_grp
    member of struct pac_grp to point to the domain struct of the configured
    for groups from this domain. This is a first step to allow group
    membership for groups from subdomains as well. For those groups a
    pointer to the related subdomain structure will be saved.