avoid lost messages after activate message

messages might get lost after activate, when the number of parameters
exceeds maxlen of the output queue, as a limited deque silently overwrites
messages.

first try: use an infinite deque, but slow down appending thread when deque
gets too big
-> does not work because the appending thread is the same

second try: increase maximum a lot, on overflow log an error message and
close connection

Change-Id: I20376f7e08240dabe43269fa63c596f07e59ddf6
Reviewed-on: https://forge.frm2.tum.de/review/20982
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/protocol/dispatcher.py

@@ -24,10 +24,10 @@
 Interface to the service offering part:
 
  - 'handle_request(connectionobj, data)' handles incoming request
-   will call 'queue_request(data)' on connectionobj before returning
+   it returns the (sync) reply, and it may call 'queue_async_reply(data)'
+   on the connectionobj
  - 'add_connection(connectionobj)' registers new connection
  - 'remove_connection(connectionobj)' removes now longer functional connection
- - may at any time call 'queue_async_request(connobj, data)' on the connobj
 
 Interface to the modules:
  - add_module(modulename, moduleobj, export=True) registers a new module under the
@@ -286,7 +286,7 @@ class Dispatcher(object):
     def handle_request(self, conn, msg):
         """handles incoming request
 
-        will call 'queue_async_request(data)' on conn or return reply
+        will call 'queue_async_reply(data)' on conn or return reply
         """
         self.log.debug(u'Dispatcher: handling msg: %s' % repr(msg))