Modified the error when SECRET_KEY is missing to be a DeprecationWarning.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17616 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/conf/__init__.py

@@ -107,7 +107,7 @@ class Settings(BaseSettings):
                 setattr(self, setting, setting_value)
 
         if not self.SECRET_KEY:
-            raise ValueError("The SECRET_KEY setting mustn't be empty.")
+            raise DeprecationWarning("The SECRET_KEY setting must not be empty.")
 
         if hasattr(time, 'tzset') and self.TIME_ZONE:
             # When we can, attempt to validate the timezone. If we can't find