title: PyDev doesn't recognise PyQt5
body: <p>I am following a tutorial on pyqt, and got this code:</p>
  
  <pre><code>import sys
  from PyQt5.QtCore import *
  from PyQt5.QtGui import *
  from PyQt5.QtWidgets import *
  
  class Example(QWidget):
  
      def __init__(self):
          super(Example, self).__init__()
          self.initUI()
  
      def initUI(self):
          cb = QCheckBox('Show title', self)
          cb.move(20, 20)
          cb.toggle()
          cb.stateChanged.connect(self.changeTitle)
  
          self.setGeometry(300, 300, 250, 150)
          self.setWindowTitle('Checkbox')
          self.show()
  
      def changeTitle(self, state):
          if state == Qt.Checked:
              self.setWindowTitle('Checkbox')
          else: self.setWindowTitle('Unchecked!')
  
  def main():
      app = QApplication(sys.argv)
      ex = Example()
      sys.exit(app.exec_())
  
  if __name__ == '__main__':
      main()
  </code></pre>
  
  <p>I'm using PyDev on Eclipse. Suffice it to say that the code runs fine, but what is awkward is that PyDev underlines anything Qt/Q with a red line which when hovered over says <code>Undefined variable: &lt;..&gt;</code>. If it is undefined then how is it that my code runs without errors? Clearly this ought to be a problem with PyDev. I've removed the python interpreter (it was pointing to python2.7 instead of 3.4) and readded it as the correct version; but that didn't work. Interestingly enough, it recognises PyQt4 and insists on using widgets from that instead of PyQt5. </p>
  
  <p>Just so you guys are aware, the code sample above is from another laptop which had PyQt5 as well. Both projects were from PyDev, and both had Ubuntu 15.04. It's possible that my importing of the project on my current machine messed up PyDev parsing the required libraries. Does anyone have a solution as to why PyDev doesn't recognise PyQt5?</p>