change config to not cache by default, unless overridden by server-specific settings.py

--HG--
branch : cache_separation

util/cache.py

@@ -6,6 +6,7 @@ Note that 'default' is being preserved for user session caching, which we're
 not migrating so as not to inconvenience users by logging them all out.
 """
 from django.core import cache
+import settings
 
 # If we can't find a 'general' CACHE defined in settings.py, we simply fall back
 # to returning the default cache. This will happen with dev machines.