Merge changes made in Gnus trunk.

Merge changes made in Gnus trunk.

shr-color.el (shr-color-visible): Really return original background if fixed.
shr.el (shr-insert-color-overlay): Replace deprecated syntax.
shr.el (shr-tag-body, shr-descend): Add background support.
shr.el (shr-tag-title): Add.
gnus-sum.el (gnus-summary-articles-in-thread): Fix a bug that causes this function to return incorrect results.
shr.el (shr-parse-style): Drop !important from styles.
message.el (message-goto-body): Remove the <#secure special-casing, which is too special.
mm-util.el (mm-enable-multibyte): Use `to' instead of t.  This fixes something or other in Emacs 23, and is backwards compatible.
message.el (message-goto-body): Use called-interactively-p.
message.el (message-in-body-p): message-goto-body returns point.
nnimap.el (nnimap-request-move-article): It's no longer necessary to clear marks before moving, since they're synced from the Gnus side first.
gnus-sum.el (gnus-summary-push-marks-to-backend): New function.
gnus-sum.el (gnus-summary-move-article): Copy over all marks before moving, so that IMAP doesn't think a new article has arrived.
message.el (message-goto-body): called-interactively-p needs a parameter, so use `any'.
gnus-cache.el (gnus-summary-insert-cached-articles): Use it.
gnus-sum.el (gnus-summary-include-articles): New function.
shr.el (shr-tag-table, shr-render-td): Add bgcolor support.
shr-color.el (shr-color-visible): Fix docstring.
shr.el (shr-insert-background-overlay): Fix typo.
shr.el (shr-render-td): Copy the background before rendering.