* gnus-registry.el (gnus-registry-save, gnus-registry-cache-save)

* gnus-registry.el (gnus-registry-save, gnus-registry-cache-save)
(gnus-registry-remove-alist-text-properties, gnus-registry-action)
(gnus-registry-split-fancy-with-parent)
(gnus-registry-fetch-simplified-message-subject-fast)
(gnus-registry-fetch-sender-fast, gnus-registry-store-extra-entry):
remove text properties on ingress into the registry and when it's saved
(gnus-registry-clean-empty-function): fixed bug with cleaning the
registry from entries with no groups

* gnus-util.el (gnus-string-remove-all-properties): utility function to
remove string properties