The purpose of this plugin is to pass "status message" between screens
through the following mechanisms:

- Stores messages in the "$c->session" so that the application is
  free to redirect to the appropriate URL after an action is taken.

- Associates a random 8-digit "token" with each messages, so it's
  completely unambiguous what message should be shown in each
  window/tab.

- Only requires that the token (not the full message) be included in
  the redirect URL.

- Automatically removes the message after the first time it is
  displayed.  That way, if users hit refresh in their browsers they
  only see the messages the first time.
