title: how to add QDockWidget to QFrame in PyQt4
body: <p>How do I add <code>QDockWidget</code> to <code>QFrame</code> ? since QFrame does not have <code>addDockWidget</code> !!!</p>
  
  <pre class="lang-py prettyprint-override"><code>from PyQt4.QtCore import *
  from PyQt4.QtGui import *
  import sys
  
  app = QApplication( sys.argv )
  
  qmainwin = QFrame()
  #qmainwin.setWindowFlags(Qt.FramelessWindowHint)
  s = QWidget()
  vboxlayout = QVBoxLayout( )
  
  spin1 = QSpinBox()
  vboxlayout.addWidget( spin1 )
  
  spin2 = QSpinBox()
  vboxlayout.addWidget( spin2 )
  s.setLayout( vboxlayout )
  
  qdock = QDockWidget( )
  qdock.setWindowFlags(Qt.FramelessWindowHint)
  qdock.setWidget( s )
  qmainwin.addDockWidget( Qt.TopDockWidgetArea, qdock )
  qmainwin.show()
  
  app.exec_()
  </code></pre>