Merge changes made in Gnus trunk.

Merge changes made in Gnus trunk.

shr.el (shr-render-td): Store the actual background colour used.
gnus-sum.el (gnus-user-date): Renamed back from gnus-summary-user-date since user code refers to it.
auth-source.el: Rewrite.
gnus.texi: Add DEVEL header (suggested by Andreas Schwab).
WEBHACKDEVEL work:
 Makefile.in (webhack, nowebhack): Hacks to produce for-the-web manuals.
 auth.texi: Use WEBHACKDEVEL.
 emacs-mime.texi: Use WEBHACKDEVEL.
 gnus.texi: Use WEBHACKDEVEL.
 message.texi: Use WEBHACKDEVEL.
 pgg.texi: Use WEBHACKDEVEL.
 sasl.texi: Use WEBHACKDEVEL.
 sieve.texi: Use WEBHACKDEVEL.
 overrides.texi: New file to set or clear WEBHACKDEVEL.
message.el (message-setup-1): Remove the read-only stuff, since it doesn't work under XEmacs, for some reason.