Merge changes made in Gnus trunk.

Merge changes made in Gnus trunk.

mml2015.el (mml2015-epg-sign): Add and use mml2015-sign-with-sender.
 (mml2015-epg-encrypt): Use mml2015-sign-with-sender.
gnus-art.el (article-update-date-lapsed): Ensure that point stays at the "same place" even if point is on the line being replaced.
 (article-update-date-lapsed): Allow updating both the combined lapsed and the lapsed headers.
 (article-update-date-lapsed): Skip past all the X-Sent/Date headers.
 (article-make-date-line): Limit the number of segments dynamically to avoid too-long lines.