title: 'Manager' object has no attribute 'create_user' in django 1.7
body: <p>Hi i am taking user's username and password in django 1.7 but i am getting error - 'Manager' object has no attribute 'create_user'</p>
  
  <p>my views.py</p>
  
  <pre><code>def register(request):
      if request.method == 'POST':
          form = UserForm(request.POST)
          if form.is_valid(): 
              post = request.POST
              username = post['username']
              email = post['email']
              password = post['password']
              user = User.objects.create_user(username, email, password)
              return redirect('/student/lastpage')
      else:
          form = UserForm()
      return render(request, 'student/register.html', {'form': form})
  </code></pre>
  
  <p>my models.py</p>
  
  <pre><code>class User(models.Model):
      username = models.CharField(max_length=20)
      password = models.CharField(max_length=30)
      email = models.CharField(max_length=50)
  
  def __str__(self):
      return self.username
  
  class UserForm(ModelForm):
      class Meta:
          model = User
          fields = '__all__'
  </code></pre>
  
  <p>any help is appreciated</p>
  
  <p>thanks in advance</p>