doc/misc/{gnus.texi,gnus-faq.texi}: Update docs wrt shr/html mail

* gnus.texi (HTML): Update section so that it mentions shr and w3m.
Also link the full EWW manual that explains more on shr, too.
* gnus-faq.texi (FAQ 4 - Reading messages, FAQ 4-16): Add Q&A on how to
increase contrast when displaying HTML mail with shr.
doc/misc/ChangeLog: Fix date for r117699
fix version tags
ChangeLog tweak
Merge from emacs-24; up to 117702
Allow VTIMEZONE where daylight and standard time zones are equal.

See: http://lists.gnu.org/archive/html/emacs-devel/2014-11/msg00494.html
* calendar/icalendar.el (icalendar--convert-tz-offset):
Support timezone without daylight saving time.