Support quotes 'like this' in info files

Support quotes 'like this' in info files

This is possible when 'makeinfo --disable-encoding' is used
in Texinfo 5.
* lisp/calc/calc-help.el (calc-describe-thing):
* lisp/gnus/gnus-art.el (gnus-button-alist):
* lisp/info.el (Info-find-index-name):
* lisp/vc/ediff-help.el (ediff-help-for-quick-help):
Also support quotes 'like this'.
* lisp/calc/calc-help.el (calc-describe-thing): Simplify.
* lisp/finder.el (finder-font-lock-keywords): Remove var that
hasn't been used in years, instead of bothering to fix its quoting.