Document renaming of x-select-enable-* variables

* doc/emacs/killing.texi (Clipboard): Rename
x-select-enable-clipboard to select-enable-clipboard and
x-select-enable-primary to select-enable-primary.  Update index
entries.

* etc/NEWS: Mark entry as documented.

doc/emacs/killing.texi

@@ -504,9 +504,9 @@ does not alter the clipboard.  However, if you change
 @code{yank-pop-change-selection} to @code{t}, then @kbd{M-y} saves the
 new yank to the clipboard.
 
-@vindex x-select-enable-clipboard
+@vindex select-enable-clipboard
   To prevent kill and yank commands from accessing the clipboard,
-change the variable @code{x-select-enable-clipboard} to @code{nil}.
+change the variable @code{select-enable-clipboard} to @code{nil}.
 
 @cindex clipboard manager
 @vindex x-select-enable-clipboard-manager
@@ -519,14 +519,14 @@ when exiting Emacs; if you wish to prevent Emacs from transferring
 data to the clipboard manager, change the variable
 @code{x-select-enable-clipboard-manager} to @code{nil}.
 
-@vindex x-select-enable-primary
+@vindex select-enable-primary
 @findex clipboard-kill-region
 @findex clipboard-kill-ring-save
 @findex clipboard-yank
   Prior to Emacs 24, the kill and yank commands used the primary
 selection (@pxref{Primary Selection}), not the clipboard.  If you
-prefer this behavior, change @code{x-select-enable-clipboard} to
-@code{nil}, @code{x-select-enable-primary} to @code{t}, and
+prefer this behavior, change @code{select-enable-clipboard} to
+@code{nil}, @code{select-enable-primary} to @code{t}, and
 @code{mouse-drag-copy-region} to @code{t}.  In this case, you can use
 the following commands to act explicitly on the clipboard:
 @code{clipboard-kill-region} kills the region and saves it to the

etc/NEWS

@@ -148,8 +148,9 @@ the `network-security-level' variable.
 +++
 ** C-h l now also lists the commands that were run.
 
-** x-select-enable-clipboard is renamed select-enable-clipboard.
-x-select-enable-primary and renamed select-enable-primary.
++++
+** x-select-enable-clipboard is renamed select-enable-clipboard
+and x-select-enable-primary is renamed select-enable-primary.
 Additionally they both now apply to all systems (OSX, GNUstep, Windows, you
 name it), with the proviso that on some systems (e.g. Windows)
 select-enable-primary is ineffective since the system doesn't