Fixed #10571 -- Factored out the payload encoding code to make sure it is used...

Fixed #10571 -- Factored out the payload encoding code to make sure it is used for PUT requests. Thanks to kennu for the report, pterk for the patch, and wildfire for the review comments.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16651 bcc190cf-cafb-0310-a4f2-bffc1f526a37