Alarm: allow chaining activities with Alarm's activeSense

activeSense() now returns the tag of the last run activity, so activeSense
can be chained with other activities.
For this, the notify() method gets its own tag. Now, when running activities
after activeSense, one is sure that it really ended.

product/ERP5/Document/Alarm.py

@@ -159,7 +159,11 @@ class Alarm(XMLObject, PeriodicityMixin):
           # Old API
           getattr(self.activate(**activate_kw), method_id)()
         if self.isAlarmNotificationMode():
-          self.activate(after_tag=tag).notify(include_active=True, params=params)
+          notification_tag=self.__getTag(True)
+          self.activate(tag=notification_tag, after_tag=tag) \
+            .notify(include_active=True, params=params)
+          return notification_tag
+        return tag
 
     # switch to nobody temporarily so that unrestricted _activeSense
     # is always invoked by system user.
@@ -170,7 +174,7 @@ class Alarm(XMLObject, PeriodicityMixin):
       activate_kw = {}
 
     try:
-      _activeSense()
+      return _activeSense()
     finally:
       # Restore the original user.
       setSecurityManager(sm)