title: pyQt QWizard change next to finish button to exit early
body: <p>Is there a way to change a next button to a finish button mid-way through a wizard if user has entered sufficient data?
  The example below uses the HaveFinishButtonOnEarlyPages set - however what I'd like to do is replace the next button with a finish button if user selects a radiobutton. Is this possible?</p>
  
  <pre><code>from PyQt4 import QtGui
  from PyQt4.QtGui import QWizard
  import sys
  
  def createPage1():
      page = QtGui.QWizardPage()
      page.setTitle("Page 1")
      page.setSubTitle("Enter some data, if you don't want to enter any more data select finish early.")
      essentialLabel = QtGui.QLabel("Essential data:")
      essentialLineEdit = QtGui.QLineEdit()
      finishEarlyRB = QtGui.QRadioButton("Select to finish wizard early")
      layout = QtGui.QGridLayout()
      layout.addWidget(essentialLabel, 0, 0)
      layout.addWidget(essentialLineEdit, 0, 1)
      layout.addWidget(finishEarlyRB, 1, 0)
      page.setLayout(layout)
      return page
  
  def createPage2():
      page = QtGui.QWizardPage()
      page.setTitle("Page 2")
      page.setSubTitle("Enter some more data.")
      nonEssentialLabel = QtGui.QLabel("Non essential data:")
      nonEssentialLineEdit = QtGui.QLineEdit()
      layout = QtGui.QGridLayout()
      layout.addWidget(nonEssentialLabel, 0, 0)
      layout.addWidget(nonEssentialLineEdit, 0, 1)
      page.setLayout(layout)
      return page
  
  if __name__ == '__main__':
      app = QtGui.QApplication(sys.argv)
      wizard = QtGui.QWizard()
      wizard.setOption(QWizard.HaveFinishButtonOnEarlyPages, on=True)
      wizard.addPage(createPage1())
      wizard.addPage(createPage2())
      wizard.show()
      sys.exit(wizard.exec_())
  </code></pre>