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/topics/checks.txt

@@ -132,13 +132,25 @@ check. Tagging checks is useful since it allows you to run only a certain
 group of checks. For example, to register a compatibility check, you would
 make the following call::
 
-    from django.core.checks import register
+    from django.core.checks import register, Tags
 
-    @register('compatibility')
+    @register(Tags.compatibility)
     def my_check(app_configs, **kwargs):
         # ... perform compatibility checks and collect errors
         return errors
 
+.. versionadded:: 1.8
+
+You can register "deployment checks" that are only relevant to a production
+settings file like this::
+
+    @register(Tags.security, deploy=True)
+    def my_check(app_configs, **kwargs):
+        ...
+
+These checks will only be run if the :djadminopt:`--deploy` option is passed to
+the :djadmin:`check` command.
+
 .. _field-checking:
 
 Field, Model, and Manager checks