Fix bug in question testing logic, update demo course and docs.

doc/en/About/Credits.md

@@ -29,6 +29,7 @@ STACK is released in many languages, using Moodle's ATOS language system.
   * EN: English (British), by Chris Sangwin (and others)
   * FI: Finnish, by Matti Pauna
   * SV: Swedish, by Mikael Kurula
+  * DA: Danish, by Malthe Sporring
   * ES: Spanish, by Victor Hugo Huerta 
   * JA: Japanese, by Yasuyuki Nakamura and Takahiro Nakahara  
 

stack/questiontestresult.php

@@ -157,16 +157,19 @@ class stack_question_test_result {
                 $state->testoutcome = false;
                 $reason[] = stack_string('score');
             }
-            // If the expected penalty is null, then we use the question default penalty.
+            // If the expected penalty is null then we use the question default penalty.
             $penalty = $state->expectedpenalty;
             if (is_null($state->expectedpenalty)) {
                 $penalty = $this->questionpenalty;
             }
+            // If we have a "NULL" expected answer note we just ignore what happens to penalties here.
+            if ('NULL' !== $state->expectedanswernote) {
                 if (is_null($state->penalty) ||
                         abs($penalty - $state->penalty) > 10E-6) {
                     $state->testoutcome = false;
                     $reason[] = stack_string('penalty');
                 }
+            }
             if (!$this->test_answer_note($state->expectedanswernote, $actualresult->answernotes)) {
                 $state->testoutcome = false;
                 $reason[] = stack_string('answernote');