Fixed #17101 -- Integrated django-secure and added check --deploy option

Thanks Carl Meyer for django-secure and for reviewing.

Thanks also to Zach Borboa, Erik Romijn, Collin Anderson, and
Jorge Carleitao for reviews.

docs/howto/deployment/checklist.txt

@@ -29,6 +29,14 @@ you're releasing the source code for your project, a common practice is to
 publish suitable settings for development, and to use a private settings
 module for production.
 
+Run ``manage.py check --deploy``
+================================
+
+Some of the checks described below can be automated using the
+:djadminopt:`--deploy` option of the :djadmin:`check` command. Be sure to run it
+against your production settings file as described in the option's
+documentation.
+
 Critical settings
 =================