Handle setting a dictionary in siteconfig's cache_backend.
Review Request #3600 — Created Dec. 1, 2012 and submitted
Handle setting a dictionary in siteconfig's cache_backend. siteconfig's cache_backend was expecting the stored data to be a string representing an old-style cache backend URI. However, when first creating a new site now, settings.CACHES will be stored in siteconfig, which breaks our bad assumptions. Now when loading from siteconfig, if cache_backend is a dictionary with a 'default' entry, we just pull from it and set it. This allows either an old-style string or a new-style CACHES info dictionary to be stored and accessed.
Unit tests pass.