Fixed #15079 -- Added a missing import in the cache infrastructure. Thanks to jaylett for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15214 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/core/cache/__init__.py

@@ -18,6 +18,7 @@ from django.conf import settings
 from django.core import signals
 from django.core.cache.backends.base import (
     InvalidCacheBackendError, CacheKeyWarning, BaseCache)
+from django.core.exceptions import ImproperlyConfigured
 from django.utils import importlib
 
 try: