Merge changes made in Gnus trunk.

Merge changes made in Gnus trunk.

message.el (message-mailto): New function.
message.el (message-mailto): Should accept other parameters.
message.el (message-mailto): Remove since it duplicates browse-url-mailto functionality.
shr.el (shr-browse-url): Call browse-url-mailto for mailto: links.
message.el (message-subject-trailing-was-ask-regexp): A ] in a [] regexp doesn't need quoting.
gnus-art.el (article-treat-non-ascii): New command and keystroke.
shr.el (browse-url-mailto): Autoload.
gnus.texi (Article Washing): Document gnus-article-treat-non-ascii.