Some minor changes in debbugs

Some minor changes in debbugs

* packages/debbugs/debbugs-gnu.el (debbugs-gnu-default-packages):
Adapt :version.
(debbugs-gnu-archived): New face.
(debbugs-gnu-show-reports): Use it.

* packages/debbugs/debbugs-ug.texi (Tabulated Lists):
Mention	`debbugs-gnu-archived'.
(Control Messages): Archived bugs must be unarchived first.

* packages/debbugs/debbugs.el (debbugs-search-est): Use `cl-case'.