Merge changes made in Gnus trunk.

Merge changes made in Gnus trunk.

gnus.el (gnus-list-debbugs): New command.
gnus-group.el (gnus-bug-group-download-format-alist): Get the mboxstat instead of the maintbox, since the stat seems to be fuller.
gnus-msg.el (gnus-configure-posting-styles): Don't try to select dead summary buffers.
message.el (message-get-reply-headers): Delete all duplicates, instead of the first.
 (message-get-reply-headers): Ensure that we have progress while deleting duplicates.
gnus-msg.el (gnus-configure-posting-styles): Get the local gnus-posting-style value from the summary buffer to make it easier to make that a per-buffer conf.