* lisp/faces.el (read-face-name): Rename arg `string-describing-default'

* lisp/faces.el (read-face-name): Rename arg `string-describing-default'
to `default'.  Doc fix.  Display the default value in quotes
in the prompt.  With empty input, return the `default' arg,
unless the default value is a string (in which case return nil).
(describe-face): Replace the string `default' arg of `read-face-name'
with the symbol `default'.
http://lists.gnu.org/archive/html/emacs-devel/2010-06/msg01109.html