Revision 1913312

Move prefix_param to the Messenger (bad name) rather than the output
mechanism. Adjust some various initialization params.

* tools/hook-scripts/mailer/mailer.py:
  (main): adjust PropChange() params -- no pool needed.
  (OutputBase.__init__): remove PREFIX_PARAM; not needed.
  (MailedOutput.mail_headers): remove PARAMS; not needed.
  (PipeOutput.__init__): remove PREFIX_PARAM; not needed. Adjust
    .mail_headers() call.
  (Messenger.__init__): remove POOL; not needed. Save PREFIX_PARAM as
    an instance variable. Adjust creation of the Output.
  (Messenger.make_subject): get .prefix_param from self, not output
  (Commit.__init__, Lock.__init__): no need to pass POOL to
    Messenger.__init__()
  (PropChange.__init__): POOL not needed at all. Drop the param.