Merge changes made in Gnus trunk.

Merge changes made in Gnus trunk.

gnus.el (gnus-sloppily-equal-method-parameters): Avoid cl.el convenience functions.
nnrss.el (nnrss-retrieve-groups): Change to the group before checking its data structures.
nnimap.el (nnimap-split-incoming-mail): Fix paren typo in the 'junk handling.
starttls.el: (starttls-open-stream): Add autoload cookie.
nnimap.el (nnimap-command): Register the last command time so that we can use it for idling NOOPs.
nnimap.el: Implement IMAP keepalive.
gnus-cache.el (gnus-cache-braid-heads): When braiding heads, don't use the same article number for all the cached articles.
nnimap.el (nnimap-update-info): Protect against nil uidnexts.
gnus-group.el: Remove the outdated archive group stuff, which no longer works.
gnus-group.el, gnus.el: Remove the outdated charter support.
gnus-sum.el, gnus-group.el, gnus.el: Remove outdated support for FAQ fetching.
gnus-gravatar.el, gravatar.el: New files.