[1.7.x] Fixed display of lists after website redesign

Thanks Brian Jacobel for the report. refs django/djangoproject.com#197

Backport of c7786550c4ed396b8580db58f7da60e850894d19 from master
[1.7x.] Fixed #23497 -- Made admin system checks run for custom AdminSites.

Backport of b7219c7ba5fdfbf9349948b5a91af50e32822ee6 from master
[1.7.x] Fixed #24007 -- Ensure apps registry's ready before unpickling models

This prevents AppRegistryNotReady errors when unpickling Django
models from an external script.
Backport of 108b8bf85 from master.