Fixes a Python 3.x regression introduced in a19e9d80
Merge pull request #1135 from ambv/model_validation_fix

Fixes a Python 3.x regression introduced in a19e9d80
Fixed #20284 - Added a note about DEBUG in static file docs.

Thanks wim@ for the suggestion and Nicolas Noé for the patch.
Fixed #13958 -- problem reporting exception from \r-line-ended file

Thanks petrvanblokland for reporting and saz for the patch
extracted prepare_lookup_and_defaults_for_get, create_or_update docstring
extracted code used on get_or_create and create_or_update, create_or_update implementation
working on tests
Working and tested implementation
Added documentation for create_or_update method
Changes requested by HonzaKral and other reviewers
Added myslef to AUTHORS
Documentation updated