* gnus.el (gnus-group-short-name, gnus-group-prefixed-p): new functions

* gnus.el (gnus-group-short-name, gnus-group-prefixed-p): new functions
(gnus-group-guess-full-name): don't prefix the group twice

* nnmail.el (nnmail-split-fancy-with-parent): docstring fix

* gnus-registry.el (gnus-registry-clear)
(gnus-registry-fetch-group, gnus-registry-grep-in-list)
(gnus-registry-split-fancy-with-parent): new functions
(gnus-register-spool-action, gnus-register-action): simplified the format
(gnus-registry): new customization group
(gnus-registry-unfollowed-groups): new variable