Fixes suggested by David Engster <deng@randomsample.de>.

Fixes suggested by David Engster <deng@randomsample.de>.

* gnus-registry.el (gnus-registry-fixup-registry): New function to
fixup the parameters that can be customized by the user between
save/read cycles.
(gnus-registry-read): Use it.
(gnus-registry-make-db): Use it.
(gnus-registry-spool-action, gnus-registry-handle-action): Fix
messaging.
(gnus-registry--split-fancy-with-parent-internal): Fix loop.
(gnus-registry-post-process-groups): Use `cond' for better messaging.
(gnus-registry-usage-test): Add subject lookup test.

* registry.el (registry-db, initialize-instance): Set up constructor
instead of :initform arguments for the sake of older Emacsen.