Fix for Instance of 'ManyToManyField' has no 'add' member. Closes #163

Disable model-no-explicit-unicode for the test class because Django 1.11
defines the AbstractBaseUser with @python_2_unicode_compatible and
we don't care about this issue for this particular test.

Author: atodorov

pylint_django/augmentations/__init__.py

@@ -244,6 +244,8 @@
 
 
 MANYTOMANY_FIELD_ATTRS = {
+    'add',
+    'clear',
     'related_name',
     'related_query_name',
     'limit_choices_to',

pylint_django/tests/input/func_noerror_manytomanyfield.py

@@ -4,6 +4,7 @@
 """
 #  pylint: disable=missing-docstring
 from django.db import models
+from django.contrib.auth.models import AbstractUser, Permission
 
 
 class Book(models.Model):
@@ -24,3 +25,28 @@ def is_author_of(self, book):
 
     def wrote_how_many(self):
         return self.wrote.count()
+
+
+# Custom permissions for CustomUser
+USER_PERMS = ['change_customuser', 'add_customuser']
+
+
+class CustomUser(AbstractUser):  # pylint: disable=model-no-explicit-unicode
+    class Meta:
+        verbose_name = 'CustomUser'
+        verbose_name_plural = 'CustomUsers'
+        app_label = "users"
+
+    def grant_permissions(self):
+        ''' Example adding permissions to User '''
+        self.user_permissions.clear()
+        for perm in USER_PERMS:
+            perm = Permission.objects.get(codename=perm)
+            self.user_permissions.add(perm)
+        return self.user_permissions
+
+    def save(self, *args, **kwargs):
+        ''' Saving while granting new permissions '''
+        self.is_staff = True
+        super(CustomUser, self).save()
+        self.grant_permissions()