Add missing migrations

What it says on the tin. With a fresh checkout of master:

```shell
$ django-admin makemigrations --settings wagtail.tests.settings
Migrations for 'tests':
  0004_auto_20141008_0420.py:
    - Delete model SearchTestOldConfig
    - Delete model SearchTestOldConfigList
Migrations for 'wagtailcore':
  0006_auto_20141008_0420.py:
    - Alter field permission_type on grouppagepermission
```