Backslash cleanup in Elisp source files

This patch should not change behavior.  It typically omits backslashes
where they are redundant (e.g., in the string literal "^\$").
In a few places, insert backslashes where they make regular
expressions clearer: e.g., replace "^\*" (equivalent to "^*") with
"^\\*", which has the same effect as a regular expression.
Also, use ‘\ %’ instead of ‘\%’ when avoiding confusion with SCCS IDs,
and similarly use ‘\ $’ instead of ‘\$’ when avoiding confusion with
RCS IDs, as that makes it clearer that the backslash is intended.

lisp/emacs-lisp/lisp-mode.el

@@ -889,7 +889,7 @@ property `lisp-indent-function' (or the deprecated `lisp-indent-hook'),
 it specifies how to indent.  The property value can be:
 
 * `defun', meaning indent `defun'-style
-  \(this is also the case if there is no property and the function
+  (this is also the case if there is no property and the function
   has a name that begins with \"def\", and three or more arguments);
 
 * an integer N, meaning indent the first N arguments specially