Fixed #21129 -- Prevented admin filter params modifications from throwing an exception.

Thanks Tuttle for the report.
Fixed #21122 -- Improved clean up of test temp directory on Windows

- Fixed test that didn't close the files it opened
- Caught and handled exception when temp directory cannot be removed
Clarified session replay attack differences with cookie backend.
Changed the doc to use gender-neutral pronouns when possible.
Fixed #10913 -- Documented how related_name affects QuerySet filtering

Thanks neithere for the suggestion.
Initial version of MigrationOptimizer and tests
Fixed #16919 -- Passed user to set_password_form in GET requests.

Thanks Jaime Irurzun for the report and initial patch and
ejucovy for the test.
Fixed #21165 -- Fix test for syndication feed timestamp field on Windows.

Thanks Michael Manfre for the report, Raphaël Barrois for the patch and
Claude Paroz, Aymeric Augustin for the reviews.

Refs #7936.