contrib/recipes/priority_queue.go
func NewPriorityQueue(client *v3.Client, key string) *PriorityQueue {
	return &PriorityQueue{client, context.TODO(), key + "/"}
}
func NewPriorityQueue(client *v3.Client, key string) *PriorityQueue {
	return &PriorityQueue{client, context.TODO(), key + "/"}
}
// NewPriorityQueue creates an etcd priority queue.