Send session_commit signal in sqlalchemy ``before_commit``.

        This marks the success of session so the session may enter commit
        state.

def session_commit(self, session):
        """Send session_commit signal in sqlalchemy ``before_commit``.

        This marks the success of session so the session may enter commit
        state.
        """
        # this may happen when there's nothing to commit
        if not hasattr(session, 'meepo_unique_id'):
            self.logger.debug("skipped - session_commit")
            return

        # normal session pub
        self.logger.debug("%s - session_commit" % session.meepo_unique_id)
        self._session_pub(session)
        signal("session_commit").send(session)
        self._session_del(session)