* lisp/gnus/nnselect.el (nnselect-generate-run): New function that
replaces nnselect-run.
(nnselect-store-artlist): New function.
(nnselect-get-artlist): Update function.
(nnselect-request-group, nnselect-request-thread)
(nnselect-request-create-group, nnselect-request-group-scan): Use the
new functions.
* doc/misc/gnus.texi (Selection Groups): Document artlist storage and
retrieval.