Merge changes made in Gnus trunk.

Merge changes made in Gnus trunk.

mm-view.el (mml-smime): Require.
mm-view.el (mm-view-pkcs7-decrypt): If mml-smime-use is set to 'epg, use EPG to decrypt S/MIME messages instead of openssl.
nnimap.el (nnimap-request-group): Avoid double SELECT on `M-g'.
gnus-group.el (gnus-group-kill-group): Don't try to update the group status is the group clearly is unreachable.
auth-source.el (auth-source-create): Add the optional second parameter to `local-variable-p' to be compatible with XEmacs.
nnml.el (nnml-request-article): Allow requesting by Message-ID to work when using a compressed nnml folder.
gnus-sum.el (gnus-select-newsgroup): Don't propagate marks to backends after sanitising on entry, because this never makes sense: If the articles have gone missing, then the data no longer exists on the backend, and if they haven't, then Gnus is wrong, and shouldn't overwrite anything anyway.
shr.el (shr-insert-document): Bind shr-width dynamically to window-width if it's nil.
shr.el (shr-width, shr-insert-document): Allow nil as shr-width value with the meaning of using the full emacs window width for rendering.