Backport commit f9acac7 from Emacs master branch

* lisp/org-clock.el (org-clock-save):
Prefer (system-name) to system-name, and avoid naming
locals 'system-name'.

system-name's returned value can vary
f9acac751d4cd22480e62cc63936b1208ca9fe48
Paul Eggert
Mon Dec 29 12:38:58 2014 -0800

lisp/org-clock.el

@@ -2813,8 +2813,8 @@ The details of what will be saved are regulated by the variable
 	  (delete-region (point-min) (point-max))
 	  ;;Store clock
 	  (insert (format ";; org-persist.el - %s at %s\n"
-			  system-name (format-time-string
-				       (cdr org-time-stamp-formats))))
+			  (system-name) (format-time-string
+					 (cdr org-time-stamp-formats))))
 	  (if (and (memq org-clock-persist '(t clock))
 		   (setq b (org-clocking-buffer))
 		   (setq b (or (buffer-base-buffer b) b))