func (peers *Peers) dereference(peer *Peer) {
	peers.Lock()
	defer peers.Unlock()
	peer.localRefCount--
}
func (peers *Peers) dereference(peer *Peer) {
	peers.Lock()
	defer peers.Unlock()
	peer.localRefCount--
}
// Dereference decrements the refcount of the matching peer.
// TODO(pb): this is an awkward way to use the mutex; consider refactoring