title: Django Many2many field Attribute Error
body: <p>I'm getting an unexpected error when trying to add data to a many2many field in a django model.  I'm not sure why I'm not getting the related data (payment_method)</p>
  
  <p>For the models below</p>
  
  <pre><code>class PaymentMethod(models.Model):
      MONTHLY_DIRECT_DEBIT = 'MDD'
      CASH_OR_CHEQUE = 'CAC'
      QUARTERLY_DIRECT_DEBIT = 'QDD'
      PAYMENT_CHOICES = (
          (MONTHLY_DIRECT_DEBIT, 'Monthly Direct Debit'),
          (CASH_OR_CHEQUE, 'Cash or Cheque'),
          (QUARTERLY_DIRECT_DEBIT, 'Quarterly Direct Debit'),
      )
      unique_id = models.CharField(max_length=3, choices=PAYMENT_CHOICES)
      name = models.CharField(max_length=255, unique=True)
  
  class Tariff(models.Model):
      name = models.CharField(max_length=255)
      supplier = models.ForeignKey(Supplier)
      payment_method = models.ManyToManyField(PaymentMethod)
      region = models.ManyToManyField(Region)
  
          class Meta:
      unique_together = ('name', 'supplier')
  
  class Supplier(models.Model):
  unique_id = models.IntegerField(unique=True)
  name = models.CharField(max_length=255, unique=True)
  </code></pre>
  
  <p>I am trying to add the payment method data to the tariff via:</p>
  
  <pre><code>supplier = Supplier.objects.get(unique_id=region.default_supplier.unique_id)
  payment_method_instance = PaymentMethod.objects.get(unique_id=payment_method['id'])
  tariff, created = Tariff.objects.get_or_create(name=tariff, supplier=supplier)
      if created:
          sys.stdout.write('Tariff {} not found for Supplier: {}\n'.format(tariff, supplier))
          tariff.payment_method.add(payment_method_instance)
  </code></pre>
  
  <p>when I try to access the tariff's payment method via the below I get the below error:</p>
  
  <pre><code>&gt;&gt;&gt; tariff1.payment_method
  Out[4]: &lt;django.db.models.fields.related_descriptors.create_forward_many_to_many_manager.&lt;locals&gt;.ManyRelatedManager at 0x11326c710&gt;
  &gt;&gt;&gt; tariff.payment_method.unique_id
  Traceback (most recent call last):
    File "", line 3066, in run_code
      exec(code_obj, self.user_global_ns, self.user_ns)
    File "&lt;ipython-input-5-a0370f309c95&gt;", line 1, in &lt;module&gt;
      tariff.payment_method.unique_id
  AttributeError: 'ManyRelatedManager' object has no attribute 'unique_id'
  </code></pre>