title: OpenMDAO Error: object has no attribute '_post_setup_vars'
body: <p>I'm building a new OpenMDAO component. I do:</p>
  
  <pre><code>prob = Problem(impl=impl, root=myNewComponent(nTurbs=4, rotor_diameter=126.0))
  prob.driver = ScipyOptimizer()
  prob.driver.add_desvar('turbineX')
  prob.driver.add_objective('AEP')
  prob.setup()
  prob.run()
  </code></pre>
  
  <p>..And OpenMDAO crashes with <code>AttributeError: 'myNewComponent' object has no attribute '_post_setup_vars'</code>. What does this message mean? </p>