Fixed #10864 -- Clarified the role played by redirect_to_field in the...

Fixed #10864 -- Clarified the role played by redirect_to_field in the login_required auth decorator. Thanks to trigeek38 for the suggestion, and SmileyChris for the draft.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@11544 bcc190cf-cafb-0310-a4f2-bffc1f526a37