* debbugs-gnu.el (debbugs-gnu-all-severities)
(debbugs-gnu-all-packages): New defconst.
(debbugs-gnu-search, debbugs-gnu): Use them.
(debbugs-gnu, debbugs-gnu-get-bugs): Handle user tags.
(debbugs-gnu-show-reports): Kill buffer initially, in order to
get rid of old local variables.
(debbugs-gnu-current-query): New defun.
(debbugs-gnu-display-status): Display also the query. Use `special-mode'.