title: Qt c++ QSystemTrayIcon not on tray, windows 7
body: <p>what am i doing wrong? Program runs and compiles but icon is not on tray.<br>
  My OS is Windows 7.</p>
  
  <pre><code>#include "mainwindow.h"
  #include "ui_mainwindow.h"
  
  MainWindow::MainWindow( QWidget * parent )
      : QMainWindow( parent )
       , ui( new Ui::MainWindow )
  {
      QMenu * trayIconMenu;
      trayIconMenu = new QMenu();
      QSystemTrayIcon tray;
      QIcon icon( ":/ok.png" );
      tray.setIcon( icon );
      tray.setContextMenu( trayIconMenu );
      tray.show();
      ui-&gt;setupUi( this );
  
  }
  
  MainWindow::~MainWindow()
  {
      delete ui;
  }
  </code></pre>