Fixed #22034 -- Added a specific set of relation checks for GenericInlineModelAdmin.

Thanks to jwa for the report.

tests/admin_checks/models.py

@@ -4,7 +4,8 @@ Tests of ModelAdmin system checks logic.
 
 from django.db import models
 from django.utils.encoding import python_2_unicode_compatible
-
+from django.contrib.contenttypes.models import ContentType
+from django.contrib.contenttypes.fields import GenericForeignKey
 
 class Album(models.Model):
     title = models.CharField(max_length=150)
@@ -55,3 +56,11 @@ class State(models.Model):
 
 class City(models.Model):
     state = models.ForeignKey(State)
+
+
+class Influence(models.Model):
+    name = models.TextField()
+
+    content_type = models.ForeignKey(ContentType)
+    object_id = models.PositiveIntegerField()
+    content_object = GenericForeignKey('content_type', 'object_id')