Fixed #13162 and #11597 -- Improved the file handling documentation: Removed...

Fixed #13162 and #11597 -- Improved the file handling documentation: Removed documentation of methods on django.core.files.File that did not exist, added documentation for undocumented methods and attributes that did exist, did a general cleanup of the text and organization, and added more metadata targets. Thanks to amenasse and tyrion.mx for the reports.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14833 bcc190cf-cafb-0310-a4f2-bffc1f526a37