Merge changes made in Gnus trunk.

Merge changes made in Gnus trunk.

gnus.texi (Window Layout): @itemize @code doesn't exist.  It's @table @code.
gnus-registry.el (gnus-registry--split-fancy-with-parent-internal): Fix logic bug.
 (gnus-registry-post-process-groups): Fix logging of no results and quote sender and subject.
network-stream.el (network-stream-open-starttls): Only do opportunistic STARTTLS upgrades if we have built-in gnutls support.  Upgrades via gnutls-cli are too slow to be done opportunistically.
gnus-start.el (gnus-get-unread-articles): Slight cleanup.
 (gnus-read-active-for-groups): Don't try to finish getting stuff where we had no early-data returned.
 (gnus-get-unread-articles): Add a sanity check so that we don't issue two async commands to the same server at the same time.
gnus-sum.el (gnus-summary-select-article-buffer): Doc fix.
gnus-registry.el (gnus-registry-remake-db): Put the warning on a "warning" level.