It can be safely commited. A big part of this does not change what the cache should do but only prepares info for cache administration page.
If Django is 1.3 with updated settings.py then the value CACHES['default']['PREFIX_KEY'] will be probably inserted twice internally to the final key in Django. This is not a problem. (It is safer than to risk insert it not once under certain circumstancies.)
If a user has Django 1.3 but has the old configuration of cache by settings.CACHE_TIMEOUT (which is necessary for use with the existing keyedcache) by applying this patch will be CACHE_TIMEOUT = 0 and _CACHE_ENABLED = False.