title: Non Boolean comparisons in flow.switch().case() Django-Viewflow
body: <p>I have a standar viewflow flow process, in one of the states id want to split my proccess based on the text value that is introduced in one of the fields. I have defined my field of interest this way in models.py</p>
  
  <p>estado_de_aprobacion= models.CharField(max_length=15, choices=REVIEW_CHOICES)</p>
  
  <p>my choices:</p>
  
  <pre><code>REVIEW_CHOICES = (
     ('APROBACION_FINAL', 'Aprobar definitivamente'),
     ('APROBACION_NUEVO_REVISOR', 'Enviar a otro revisor'),
     ('DEVOLVER_EJECUTOR','Devolver al ejecutor')
  )
  </code></pre>
  
  <p>so basically what happens is that a drop list is displayed so the user can choose one of the options, and based on that I appliy the followinf split in the flow:</p>
  
  <pre><code>split =(
          #If(lambda activation: activation.process.aprobacion_final)
          flow.Switch()
          .Case(this.end, cond=((lambda act: act.process.estado_de_aprobacion)=='APROBACION_FINAL'))
          .Case(this.revisor_check, cond=((lambda act: act.process.estado_de_aprobacion)=='APROBACION_NUEVO_REVISOR'))
          .Case(this.ejecutar, cond=((lambda act: act.process.estado_de_aprobacion)=='DEVOLVER_EJECUTOR'))
      )
  </code></pre>
  
  <p>I assume that the lamba expression returns the value contained in the specified proccess atributes but since the comparisson isn't working im thinking its wrong.</p>