Fixed #2070: refactored Django's file upload capabilities.

      A description of the new features can be found in the new [http://www.djangoproject.com/documentation/upload_handing/ upload handling documentation]; the executive summary is that Django will now happily handle uploads of large files without issues.

This changes the representation of uploaded files from dictionaries to bona fide objects; see BackwardsIncompatibleChanges for details.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7814 bcc190cf-cafb-0310-a4f2-bffc1f526a37