Bug in message disassociation

* gnorb-gnus.el (gnorb-gnus-incoming-do-todo): Wrong local variable.
Always clear attachments during triggering

* gnorb-utils.el (gnorb-trigger-todo-action):
  `gnorb-gnus-capture-attachments' needs to be set to nil even if there
  are errors. Leaving that variable populated, even if the trigger
  process fails/aborts, can be very confusing.