fixed #131

and display an error if a reporter or a “called” ring is missing a
“report” statement

history.txt

@@ -2349,3 +2349,4 @@ ______
 * Objects: Fixed #372
 * Threads: Fixed #644
 * Store: Fixed #34
+* Threads: Fixed #131

threads.js

@@ -698,7 +698,7 @@ Process.prototype.doYield = function () {
 
 Process.prototype.exitReporter = function () {
     // catch-tag for REPORT and STOP BLOCK primitives
-    this.popContext();
+    this.handleError(new Error("missing 'report' statement in reporter"));
 };
 
 // Process Exception Handling
@@ -1098,6 +1098,7 @@ Process.prototype.evaluateCustomBlock = function () {
                 outer.receiver
             );
             runnable.parentContext = exit;
+            this.popContext(); // don't yield when done
         } else {
             // tag all "stop this block" blocks with the current
             // procedureCount as exitTag, and mark all "report" blocks