Disable ido completion in org-set-tags

This is a workaround for #156. It should be reverted if #156 is fixed
properly.

ido-completing-read+.el

@@ -294,7 +294,9 @@ disable fallback based on collection size, set this to nil."
     ;; https://github.com/DarwinAwardWinner/ido-completing-read-plus/issues/39
     Info-read-node-name
     ;; https://github.com/DarwinAwardWinner/ido-completing-read-plus/issues/44
-    tmm-prompt)
+    tmm-prompt
+    ;; https://github.com/DarwinAwardWinner/ido-completing-read-plus/issues/156
+    org-tags-completion-function)
   "Functions & commands for which ido-cr+ should be disabled.
 
 Each entry can be either a symbol or a string. A symbol means to