Freezing zombie channels into a list avoids RuntimeError

Fixes Supervisor#1178 which says that a ___RuntimeError__ is raised when the dictionary size changes during iteration.  This change freezes dict.values() into a list before the loop begins so that the list will not change during iteration.

Author: cclauss

supervisor/medusa/http_server.py

@@ -506,7 +506,7 @@ def maintenance (self):
 
     def kill_zombies (self):
         now = int (time.time())
-        for channel in asyncore.socket_map.values():
+        for channel in list(asyncore.socket_map.values()):
             if channel.__class__ == self.__class__:
                 if (now - channel.last_used) > channel.zombie_timeout:
                     channel.close()