Alarm_acceptSubmittedCredentialList: Activate "accept" transition.

This removes the need for limitting the number of documents to
process in a single transaction, thanks to searchAndActivate.
Also, handle catalog desynchronisation gracefuly in the event
of accept/accept race condition.
credential_interaction_workflow/scripts/Call_alarmActiveSense: Simplify.

Save one reindexation activity if alarm is not triggered.
Drop single-use locals.
Drop comment telling what the code already expresses.
CMFActivity: Set transaction user and note when executing Message.

In normal Zope usage, ZPublisher does this. TimerServer does not provide
publisher with a request (which would be irrelevant anyway), so
CMFActivity-managed transactions notes are empty.
Notes are useful to identify the cause of an object modification, so set
them in CMFActivity.
support 304 (Not Modified) response where we support caching policy manager.