Fixed #20733 -- Typo in docs/ref/class-based-views/generic-display.txt

Thanks ijl20@ for the report.
Fixed #13721 -- Added UploadedFile.content_type_extra.

Thanks Waldemar Kornewald and mvschaik for work on the patch.
Fixed #20429 -- Added QuerySet.update_or_create

Thanks tunixman for the suggestion and Loic Bistuer for the review.