Add Unique Queue infrastructure and move TestPullRequests to this (#9856)

* Upgrade levelqueue to version 0.2.0

This adds functionality for Unique Queues

* Add UniqueQueue interface and functions to create them

* Add UniqueQueue implementations

* Move TestPullRequests over to use UniqueQueue

* Reduce code duplication

* Add bytefifos

* Ensure invalid types are logged

* Fix close race in PersistableChannelQueue Shutdown

vendor/gitea.com/lunny/levelqueue/README.md

@@ -25,4 +25,36 @@ data, err = queue.LPop()
 queue.LHandle(func(dt []byte) error{
     return nil
 })
-```
+```
+
+You can now create a Set from a leveldb:
+
+```Go
+set, err := levelqueue.OpenSet("./set")
+
+added, err:= set.Add([]byte("member1"))
+
+has, err := set.Has([]byte("member1"))
+
+members, err := set.Members()
+
+removed, err := set.Remove([]byte("member1"))
+```
+
+And you can create a UniqueQueue from a leveldb:
+
+```Go
+queue, err := levelqueue.OpenUnique("./queue")
+
+err := queue.RPush([]byte("member1"))
+
+err = queue.LPush([]byte("member1"))
+// Will return ErrAlreadyInQueue
+
+// and so on.
+```
+
+## Creating Queues, UniqueQueues and Sets from already open DB
+
+If you have an already open DB you can create these from this using the
+`NewQueue`, `NewUniqueQueue` and `NewSet` functions.