Backport commit ef144113f from Emacs

* lisp/org-protocol.el (org-protocol-flatten): Make it an alias for
flatten-tree if available.

Some more flatten-tree aliases
ef144113f3473f39d3df3e96e780c832e0d5420e
Paul Eggert
Mon Dec 17 10:26:15 2018 -0800

lisp/org-protocol.el

@@ -350,17 +350,20 @@ returned list."
 	  ret)
       l)))
 
-(defun org-protocol-flatten (list)
-  "Transform LIST into a flat list.
+(if (fboundp 'flatten-tree)
+    (defalias 'org-protocol-flatten 'flatten-tree)
+  (defun org-protocol-flatten (list)
+    "Transform LIST into a flat list.
 
 Greedy handlers might receive a list like this from emacsclient:
 \((\"/dir/org-protocol:/greedy:/~/path1\" (23 . 12)) (\"/dir/param\"))
 where \"/dir/\" is the absolute path to emacsclients working directory.
 This function transforms it into a flat list."
-  (if (null list) ()
-    (if (listp list)
-	(append (org-protocol-flatten (car list)) (org-protocol-flatten (cdr list)))
-      (list list))))
+    (if (null list) ()
+      (if (listp list)
+	  (append (org-protocol-flatten (car list))
+                  (org-protocol-flatten (cdr list)))
+        (list list)))))
 
 (defun org-protocol-parse-parameters (info &optional new-style default-order)
   "Return a property list of parameters from INFO.