general: make sure context processors are applied in ajax rendering (#10345)

As Django 1.8 now supports several template engines the template context
processors are only applied when the context is bound to an actual template;
trick it here as a stopgap measure as we continue to support both Django 1.7
and 1.8.

combo/public/views.py

@@ -17,6 +17,7 @@
 import urllib
 import urlparse
 
+import django
 from django.conf import settings
 from django.contrib import messages
 from django.contrib.auth import logout as auth_logout
@@ -25,7 +26,7 @@ from django.core.exceptions import ObjectDoesNotExist, PermissionDenied
 from django.http import (Http404, HttpResponse, HttpResponseRedirect,
         HttpResponsePermanentRedirect)
 from django.shortcuts import render, resolve_url
-from django.template import RequestContext
+from django.template import RequestContext, loader
 from django.utils.translation import ugettext as _
 from django.forms.widgets import Media
 
@@ -83,7 +84,16 @@ def ajax_page_cell(request, page_pk, cell_reference):
             # Cell can pass data through its own __dict__
             cell.modify_global_context(context, request)
 
-    return HttpResponse(cell.render(context), content_type='text/html')
+    if django.VERSION < (1, 8, 0):
+        return HttpResponse(cell.render(context), content_type='text/html')
+    else:
+        # FIXME: we bind to an existing template to have the list of
+        # context processors applied to the RequestContext; the
+        # CellBase.render() method should be extended to accept an additional
+        # request parameter, to match the new Template::render() signature.
+        template = loader.get_template('combo/page_template.html')
+        with context.bind_template(template.template):
+            return HttpResponse(cell.render(context), content_type='text/html')
 
 
 def extend_with_locked_placeholders_cells(cells, page, pages):