gnus-sum.el (gnus-summary-select-article): Make sure we have the original article...

gnus-sum.el (gnus-summary-select-article): Make sure we have the original article buffer live.
gnus-sum.el (gnus-summary-select-article-buffer): Mention gnus-widen-article-buffer.
shr.el (shr-tag-object): Added.
nnir.el, gnus-group.el: Make nnir work by default.
gnus-agent.el (gnus-agent-fetch-group): Don't download stuff if the group isn't covered by the agent.
gnus-sum.el (gnus-group-make-articles-read): Propagate marks to the backend for unknown groups.
gnus-html.el (gnus-html-prefetch-images): Decode entities before prefetching images.