title: Using customuser in django as foreignkey to model leads to .OperationalError: (1005, "Can't create table (errno: 150)")
body: <p>I have created a custom user in my django project that inherits from AbstractBaseUser and PermissionsMixin.</p>
  
  <pre><code>class CustomUserManager(BaseUserManager):
  
      def _create_user(self, username,  password, is_staff, is_superuser, email=None, **extrafields):
          now = timezone.now()
          if not username:
              raise ValueError("You must specify a username first")
          if email:
              email = self.normalize_email(email)
  
          user = self.model(username=username, email=email, is_superuser=is_superuser,
                        is_staff=is_staff, is_active=True, last_login=now,
                        date_joined=now, **extrafields)
  
          user.set_password(password)
          user.save(self._db)
          return user
  
      def create_user(self, username, password=None,  email=None, **extrafields):
           return self._create_user(username, password, False, False, email=email, **extrafields)
  
      def create_superuser(self, username, password, email=None, **extrafields):
          return self._create_user(username, password, True, True, email=email, **extrafields)
  
  
  class MyCustomUser(AbstractBaseUser, PermissionsMixin):
      username = models.CharField(max_length=30, unique=True)
      email = models.EmailField(_("email address"), max_length=254, unique=True, blank=True, null=True)
      first_name = models.CharField(max_length=30, blank=True)
  
      #more custom user fields
  </code></pre>
  
  <p>I have set the settings attribute </p>
  
  <pre><code>settings.AUTH_USER_MODEL = "users.MyCustomUser"
  </code></pre>
  
  <p>and used this user as a ForeignKey to another model</p>
  
  <pre><code>class Customer(models.Model):
  
      creator =  models.ForeignKey(settings.AUTH_USER_MODEL)
      another_model = models.ForeignKey(AnotherModel)
  </code></pre>
  
  <p>When I run the migrate function it gives me the error described on the title. If i comment out creator field it works (so only the creator foreignkey is causing an issue). I didn't have this problem with sqlite3 and and Django 1.6. I am now in Django 1.8.x and changed to MySQL (locally for developement)and having this issue. Has something changed?</p>