title: Prevent dialogs and alerts while showing a progress bar in InDesign CC JavaScript
body: <p>My script analyses a bunch of InDesign files. Any warnings about missing fonts etc are irrelevant, thus I turn off user interaction during the core work:</p>
  
  <pre><code>// preparation code
  app.scriptPreferences.userInteractionLevel = UserInteractionLevels.NEVER_INTERACT;
  // core work code
  app.scriptPreferences.userInteractionLevel = UserInteractionLevels.INTERACT_WITH_ALL;
  // finish code
  </code></pre>
  
  <p>Nevertheless I want to show a progress bar. I've set this up with ScriptUI:</p>
  
  <pre><code>progressPanel = new ProgressPanel(files.length, 500);
  progressPanel.show();
  
  for (i = 0; i &lt; files.length; i++) {
      processFile( files[i] );
      progressPanel.incr();
      progressPanel.setText( files[i].name );
      progressPanel.show();
  }
  
  // Progress Panel, inspired from:
  // http://wwwimages.adobe.com/content/dam/Adobe/en/devnet/indesign/sdk/cs6/scripting/InDesign_ScriptingGuide_JS.pdf
  // We make it a class.
  function ProgressPanel (myMaximumValue, myProgressBarWidth){
      this.myProgressPanel = new Window('window', 'analyse InDesign files…');
      this.value = 0;
  
      this.myProgressPanel.myProgressBar
          = this.myProgressPanel.add('progressbar', 
                                   [12, 12, myProgressBarWidth, 24], 
                                      0, myMaximumValue);
      this.myProgressPanel.myText
          = this.myProgressPanel.add("statictext", 
                                     [15, 6, myProgressBarWidth, 24]);    
      this.show = function() {
          this.myProgressPanel.show();
      }
      this.hide = function() {
          this.myProgressPanel.hide();
      }
      this.setValue = function(value) {
          this.value = value;
          this.myProgressPanel.myProgressBar.value = value;
      }
      this.incr = function() {
          var inc = arguments.length ? arguments[0] : 1;
          this.value += inc;
          this.myProgressPanel.myProgressBar.value = this.value;
      }
      this.setText = function(text) {
          this.myProgressPanel.myText.text = text;
      }
  }
  </code></pre>
  
  <p>This works fine in InDesign CS 6. But not in CC 2015, unless I remove all NEVER_INTERACT statements.</p>
  
  <p>How can I show my progress bar while suppressing other user interaction, in both InDesign CS 6 and later?</p>