org-clock: Update syntax for indentation in clock tables

* lisp/org-clock.el (org-clocktable-indent-string): Use "\emsp"
  instead of "\__", which is not supported anymore since Org 8.0.

Thanks to Buddy Butterfly for reporting it.
http://permalink.gmane.org/gmane.emacs.orgmode/88842

lisp/org-clock.el

@@ -2556,13 +2556,10 @@ from the dynamic block definition."
     total-time))
 
 (defun org-clocktable-indent-string (level)
-  (if (= level 1)
-      ""
-    (let ((str "\\__"))
-      (while (> level 2)
-	(setq level (1- level)
-	      str (concat str "___")))
-      (concat str " "))))
+  (if (= level 1) ""
+    (let ((str " "))
+      (dotimes (k (1- level) str)
+	(setq str (concat "\\emsp" str))))))
 
 (defun org-clocktable-steps (params)
   "Step through the range to make a number of clock tables."