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/easy-mmode.el

@@ -136,7 +136,7 @@ BODY contains code to execute each time the mode is enabled or disabled.
 :variable PLACE	The location to use instead of the variable MODE to store
 		the state of the mode.	This can be simply a different
 		named variable, or a generalized variable.
-		PLACE can also be of the form \(GET . SET), where GET is
+		PLACE can also be of the form (GET . SET), where GET is
 		an expression that returns the current state, and SET is
 		a function that takes one argument, the new state, and
 		sets it.  If you specify a :variable, this function does