org-capture: Fix interactive template placeholders

* lisp/org-capture.el (org-capture-fill-template): Allow spaces in
  interactive placeholders.

Reported-by: Charles Millar <millarc@verizon.net>
<http://permalink.gmane.org/gmane.emacs.orgmode/104113>

lisp/org-capture.el

@@ -1760,7 +1760,7 @@ The template may still contain \"%?\" for cursor positioning."
 			(member key '("u" "U"))
 			nil nil (list org-end-time-was-given))))
 		    (_
-		     (push (completing-read
+		     (push (org-completing-read
 			    (concat (or prompt "Enter string")
 				    (and default (format " [%s]" default))
 				    ": ")