instantiate a job instead of fetch

this removes the need for the depended on job.id already being saved

rq/queue.py

@@ -190,7 +190,7 @@ class Queue(object):
         # modifying the dependency. In this case we simply retry
         if depends_on is not None:
             if not isinstance(depends_on, self.job_class):
-                depends_on = Job.fetch(id=depends_on, connection=self.connection)
+                depends_on = Job(id=depends_on, connection=self.connection)
             with self.connection.pipeline() as pipe:
                 while True:
                     try: