Added the possibility to pass a stdin object to a management command.

This makes testing certain features easier.

Thanks to AeroNotix for the original patch.

django/core/management/base.py

@@ -306,6 +306,7 @@ class BaseCommand(object):
             self.stderr = OutputWrapper(options.get('stderr', sys.stderr))
         else:
             self.stderr = OutputWrapper(options.get('stderr', sys.stderr), self.style.ERROR)
+        self.stdin = options.get('stdin', sys.stdin)  # Useful for testing
 
         if self.can_import_settings:
             from django.conf import settings  # NOQA