'Create a new roster.
Arguments:
xmpp -- The main SleekXMPP instance.
db   -- Optional interface object to a datastore.'

def __init__(self, xmpp, db=None):

    self.xmpp = xmpp
    self.db = db
    self._auto_authorize = True
    self._auto_subscribe = True
    self._rosters = {}
    if self.db:
        for node in self.db.entries(None, {}):
            self.add(node)
    self.xmpp.add_filter('out', self._save_last_status)
