title: Get HWND on windows with Qt5 (from WId)
body: <p>I am trying to convert a Qt4 Application to Qt5.
  The only thing I couldn't figure out is how to get the <em>HWND</em> of a Widget.
  The program uses <a href="https://code.google.com/p/dukto/downloads/detail?name=EcWin7-1.0.2.zip&amp;can=2&amp;q=" rel="noreferrer">EcWin7</a> to show the progress on the taskbar icon on win 7+ but expects a <em>HWND</em>. The lib itself seems to compile fine after changing <em>Q_WS_WIN</em> to <em>Q_OS_WIN</em>)
  In Qt4 on Windows <em>WId</em> was just a typedef for <em>HWND</em>, so this was no problem.
  In Qt5 this is not the case anymore.
  I found some <a href="http://comments.gmane.org/gmane.comp.lib.qt.user/4895" rel="noreferrer">mailing list posting</a> that could give a clue but it seems <em>QPlatformNativeInterface</em> is not part of the public API of Qt5 anymore.</p>
  
  <p>The program calls <em>EcWin7.init(this->winId());</em> and I need to some way to convert this ID into the <em>HWND</em> id or some other way to get this.</p>