Return value
     array - a two dimensional, nested array
     indicated by the name of the newsgroup, every entry contains
     information about the newsgroup:
     
        $groups[newsgroup_name]['group']
        name of the newsgroup
       
        $groups[newsgroup_name]['last']
        message number of the last message
       
        $groups[newsgroup_name]['first']
        message number of the first message
       
        $groups[newsgroup_name]['posting_allowed']
        values: y - yes, 
        n - no,
        m - moderated)
       
        $groups[newsgroup_name]['desc']
        newsgroup description