(help-fns--first-release): Try and avoid false positives

(help-fns--first-release): Try and avoid false positives

We used to use a very "optimistic" regexp which worked well for
longish symbol names but suffered from too many false positives on
short names.  Use a more restrictive regexp, which should make the
recent "weed out" change unnecessary.

This in turn requires the use of '...' more consistently in etc/NEWS* files.

* lisp/help-fns.el (help-fns--first-release-regexp): New function.
(help-fns--first-release): Use it.  Fix minor issue with the Emacs
version regexp.
(help-fns--mention-first-release): Undo last change.

* etc/NEWS*: Replace `...' with '...'.  Indent code examples by at
least 2 spaces. Add previously missing '...' quotes around many of
the variables and functions described.