checkCommitLock2On{Abort,Commit}.  When
ZEOStorage.notifyDisconnected() calls self.tpc_abort(), it is possible
that self.strategy is DelayedCommitStrategy.  In that case,
ZEOStorage.tpc_abort() should *not* call self._handle_waiting(),
otherwise there could be two ZEOStorage instances whose strategy is
ImmediateCommitStrategy!