babel: Make `org-babel-execute-subtree' support prefix arg

	* ob.el (org-babel-execute-subtree): Pass prefix arg through
	to `org-babel-execute-src-block'

lisp/ob.el

@@ -583,7 +583,7 @@ the current subtree."
   (save-restriction
     (save-excursion
       (org-narrow-to-subtree)
-      (org-babel-execute-buffer)
+      (org-babel-execute-buffer arg)
       (widen))))
 
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