Rename registry timeout to registry ttl

This matches job.cleanup() better and (I think) makes the purpose slightly clearer.

rq/registry.py

@@ -27,9 +27,9 @@ class BaseRegistry(object):
         self.cleanup()
         return self.connection.zcard(self.key)
 
-    def add(self, job, timeout, pipeline=None):
-        """Adds a job to a registry with expiry time of now + timeout."""
-        score = timeout if timeout < 0 else current_timestamp() + timeout
+    def add(self, job, ttl, pipeline=None):
+        """Adds a job to a registry with expiry time of now + ttl."""
+        score = ttl if ttl < 0 else current_timestamp() + ttl
         if pipeline is not None:
             return pipeline.zadd(self.key, score, job.id)