Swap out (again) jstrencode for jstrdecode

This happened because when focusing on a bug for several days that had
to do with decoding code points (which so happens to be encoding but in
JSON it should be converted to unicode even when decoding) I lost sight
of the fact that jstrencode is meant to be **JSON** encoder. In the
process of this I have uncovered a number of other bugs but that's with
jstrencode and the website uses jstrdecode so this should not delay the
contest at all.

bin/subst.default.sh

@@ -290,7 +290,7 @@ echo "DOCROOT_SLASH=$DOCROOT_SLASH"
 export VALIDATOR_ENCODED_URL
 
 
-# output the Validator encoded URL
+# output the Validator decoded URL
 #
 echo "-s"
 echo "VALIDATOR_ENCODED_URL=$VALIDATOR_ENCODED_URL"