Restrict fullscreen feature to X-based systems.

Recent Emacs in OSX already comes with fullscreen support.

core/prelude-core.el

@@ -514,13 +514,17 @@ With numeric prefix arg DEC, decrement the integer by DEC amount."
   (interactive "p")
   (prelude-increment-integer-at-point (- (or dec 1))))
 
-(defun prelude-fullscreen ()
+;;; Emacs in OSX already has fullscreen support
+(when (eq window-system 'x)
+  (defun prelude-fullscreen ()
     "Makes Emacs window fullscreen.
 
-This follows freedesktop standards."
+This follows freedesktop standards, should work in X servers."
     (interactive)
     (x-send-client-message nil 0 nil "_NET_WM_STATE" 32
                            '(2 "_NET_WM_STATE_FULLSCREEN" 0)))
+  (global-set-key (kbd "<f11>") 'prelude-fullscreen)
+)
 
 (provide 'prelude-core)
 ;;; prelude-core.el ends here

core/prelude-global-keybindings.el

@@ -96,9 +96,6 @@
 ;; replace buffer-menu with ibuffer
 (global-set-key (kbd "C-x C-b") 'ibuffer)
 
-;; make window fullscreen
-(global-set-key (kbd "<f11>") 'prelude-fullscreen)
-
 ;; toggle menu-bar visibility
 (global-set-key (kbd "<f12>") 'menu-bar-mode)