identity, ignore: Make arg names more consistent with docs

* lisp/subr.el (ignore): Rename argument IGNORE to ARGUMENTS.

* src/fns.c (Fidentity): Rename ARG to ARGUMENT.

* doc/lispref/functions.texi (Calling Functions): Fix references.

doc/lispref/functions.texi

@@ -929,12 +929,12 @@ that accept function arguments are often called @dfn{functionals}.
 function as the argument.  Here are two different kinds of no-op
 function:
 
-@defun identity arg
-This function returns @var{arg} and has no side effects.
+@defun identity argument
+This function returns @var{argument} and has no side effects.
 @end defun
 
-@defun ignore &rest args
-This function ignores any arguments and returns @code{nil}.
+@defun ignore &rest arguments
+This function ignores any @var{arguments} and returns @code{nil}.
 @end defun
 
   Some functions are user-visible @dfn{commands}, which can be called

lisp/subr.el

@@ -332,9 +332,9 @@ PREFIX is a string, and defaults to \"g\"."
                (setq gensym-counter (1+ gensym-counter)))))
     (make-symbol (format "%s%d" (or prefix "g") num))))
 
-(defun ignore (&rest _ignore)
+(defun ignore (&rest _arguments)
   "Do nothing and return nil.
-This function accepts any number of arguments, but ignores them."
+This function accepts any number of ARGUMENTS, but ignores them."
   (interactive)
   nil)
 

src/fns.c

@@ -49,11 +49,11 @@ static bool internal_equal (Lisp_Object, Lisp_Object,
 			    enum equal_kind, int, Lisp_Object);
 
 DEFUN ("identity", Fidentity, Sidentity, 1, 1, 0,
-       doc: /* Return the argument unchanged.  */
+       doc: /* Return the ARGUMENT unchanged.  */
        attributes: const)
-  (Lisp_Object arg)
+  (Lisp_Object argument)
 {
-  return arg;
+  return argument;
 }
 
 DEFUN ("random", Frandom, Srandom, 0, 1, 0,