fixed #1212 - Null continuation doesn't escape from calling context

gui.js

@@ -70,7 +70,7 @@ isSnapObject*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.gui = '2016-May-04';
+modules.gui = '2016-May-09';
 
 // Declarations
 
@@ -2835,7 +2835,7 @@ IDE_Morph.prototype.aboutSnap = function () {
         module, btn1, btn2, btn3, btn4, licenseBtn, translatorsBtn,
         world = this.world();
 
-    aboutTxt = 'Snap! 4.0.7.1\nBuild Your Own Blocks\n\n'
+    aboutTxt = 'Snap! 4.0.7.2\nBuild Your Own Blocks\n\n'
         + 'Copyright \u24B8 2016 Jens M\u00F6nig and '
         + 'Brian Harvey\n'
         + 'jens@moenig.org, bh@cs.berkeley.edu\n\n'

threads.js

@@ -61,7 +61,7 @@ StageMorph, SpriteMorph, StagePrompterMorph, Note, modules, isString, copy,
 isNil, WatcherMorph, List, ListWatcherMorph, alert, console, TableMorph,
 TableFrameMorph, isSnapObject*/
 
-modules.threads = '2016-May-04';
+modules.threads = '2016-May-09';
 
 var ThreadManager;
 var Process;
@@ -3332,7 +3332,7 @@ Context.prototype.continuation = function () {
     } else if (this.parentContext) {
         cont = this.parentContext;
     } else {
-        return new Context(null, 'doYield');
+        return new Context(null, 'doStop');
     }
     cont = cont.copyForContinuation();
     cont.tag = null;