Fix import errors with Django 1.6 code

polymorphic/admin/generic.py

@@ -1,10 +1,14 @@
-from django.contrib.contenttypes.admin import GenericInlineModelAdmin
 from django.contrib.contenttypes.models import ContentType
 from django.utils.functional import cached_property
 
 from polymorphic.formsets import polymorphic_child_forms_factory, BaseGenericPolymorphicInlineFormSet, GenericPolymorphicFormSetChild
 from .inlines import PolymorphicInlineModelAdmin
 
+try:
+    from django.contrib.contenttypes.admin import GenericInlineModelAdmin  # Django 1.7+
+except ImportError:
+    from django.contrib.contenttypes.generic import GenericInlineModelAdmin
+
 
 class GenericPolymorphicInlineModelAdmin(PolymorphicInlineModelAdmin, GenericInlineModelAdmin):
     """

polymorphic/admin/inlines.py

@@ -6,7 +6,6 @@ Each row in the inline can correspond with a different subclass.
 from functools import partial
 
 from django.contrib.admin.options import InlineModelAdmin
-from django.contrib.admin.utils import flatten_fieldsets
 from django.core.exceptions import ImproperlyConfigured
 from django.forms import Media
 
@@ -14,6 +13,11 @@ from polymorphic.formsets import polymorphic_child_forms_factory, BasePolymorphi
 from polymorphic.formsets.utils import add_media
 from .helpers import PolymorphicInlineSupportMixin
 
+try:
+    from django.contrib.admin.utils import flatten_fieldsets  # Django 1.7+
+except ImportError:
+    from django.contrib.admin.util import flatten_fieldsets
+
 
 class PolymorphicInlineModelAdmin(InlineModelAdmin):
     """