Merge changes made in Gnus trunk.

Merge changes made in Gnus trunk.

sieve-manage.el (sieve-manage-default-stream): Make default stream customizable.
nnimap.el (nnimap-request-accept-article): Send a "." at the end, which may or may not help.
nnimap.el (nnimap-open-connection): Have the `network' nnimap connection use STARTTLS opportunistically.
gnus-sum.el (gnus-summary-insert-new-articles): Copy the old-high watermark so that nothing alters it while scanning for new messages.
nnimap.el (nnimap-request-accept-article): Remove the "." at the end, since some servers don't like it.
nnimap.el (nnimap-open-connection): Forget credentials if the server says the password was wrong.
nnimap.el (nnimap-parse-line): Protect against invalid data.
gnus-art.el, gnus-sum.el, nnimap.el: Allow setting the partial fetch per server instead of globally.
message.el (message-cite-prefix-regexp): Revert last edit.
nnmairix.el: Make it work with latest changes in nnimap.
gnus-sum.el (gnus-summary-move-article): Don't alter gnus-newsgroup-active.
gnus-sum.el (gnus-summary-exit): Kill the article buffer later, so that you don't get flashes of other buffers.
nnimap.el: Fix up partial nnimap fetching.
gnus-sum.el: Rework the `/ N' based on the new gnus-newsgroup-highest variable.