Merge branch '6.4' into 7.2

* 6.4:
  Fix confusing wording about redeliver_timeout duration

Author: javiereguiluz

messenger.rst

@@ -1672,7 +1672,7 @@ The transport has a number of options:
 
     .. note::
 
-        Set ``redeliver_timeout`` to a greater value than your slowest message
+        Set ``redeliver_timeout`` to a greater value than your longest message
         duration. Otherwise, some messages will start a second time while the
         first one is still being handled.