Docstring fix

* gnorb-gnus.el (gnorb-gnus-incoming-do-todo): Docstring was totally out
  of date.
Fix tracking messages from virtual groups

* gnorb-utils.el (gnorb-get-real-group-name): New function for finding
  the original group name of messages in nnvirtual or nnir groups.

* gnorb-gnus.el (gnorb-gnus-incoming-do-todo): Use new function.
* gnorb-bbdb.el (gnorb-bbdb-store-message-link): Use new function.

Previously, triggering headings from messages in nnvirtual/nnir groups
would create registry entries with 'group keys pointing to the ephemeral
group name. Now we find the real group name before creating the entry.
Zap another with-eval-after-load

* gnorb-utils.el (gnorb-tracking-initialize): Switch back to
  `eval-after-load'.