Use Django 1.8 meta API in Page.copy()

Fall back to old API for Django 1.7

wagtail/wagtailcore/models.py

@@ -5,6 +5,7 @@ import json
 
 from modelcluster.models import ClusterableModel, get_all_child_relations
 
+import django
 from django.db import models, connection, transaction
 from django.db.models import Q
 from django.db.models.signals import post_save, pre_delete, post_delete
@@ -769,9 +770,26 @@ class Page(six.with_metaclass(PageBase, MP_Node, ClusterableModel, index.Indexed
         specific_self = self.specific
         specific_dict = {}
 
-        for field in specific_self._meta.fields:
-            if field.name not in exclude_fields and not (field.rel is not None and field.rel.parent_link):
+        if django.VERSION >= (1, 8):
+            for field in specific_self._meta.get_fields():
+                # Ignore explicitly excluded fields
+                if field.name in exclude_fields:
+                    continue
+
+                # Ignore reverse relations
+                if field.auto_created:
+                    continue
+
+                # Ignore parent links (page_ptr)
+                if isinstance(field, models.OneToOneField) and field.parent_link:
+                    continue
+
                 specific_dict[field.name] = getattr(specific_self, field.name)
+        else:
+            # Django 1.7
+            for field in specific_self._meta.fields:
+                if field.name not in exclude_fields and not (field.rel is not None and field.rel.parent_link):
+                    specific_dict[field.name] = getattr(specific_self, field.name)
 
         # New instance from prepared dict values, in case the instance class implements multiple levels inheritance
         page_copy = self.specific_class(**specific_dict)