[1.5.x] Fixed #20482 - Added a file reference in tutorial 3.

Thanks diek@ for the suggestion.

Backport of 9e65bd33db from master
[1.5.x] Fixed #20417 - Noted that a server restart is required to load new templatetag modules.

Thanks Katya for the suggestion.

Backport of a46a399534 from master
[1.5.x] Fixed #20316 - Clarified transaction behavior of TestCase.

Thanks uberj@ for the report and lolek09 for the patch.

Backport of dffdca1109 from master
[1.5.x] Updated link to jQuery Cookie plugin site

Backport of 81f454a322 from master
[1.5.x] Fixed #20492 - Removed a broken link in GIS docs.

Backport of fbab3209fc from master
[1.5.x] Rotate CSRF token on login

Backport of 1514f17aa60772f48839130f9a5071b9ffe15213 from master
Fix for issue #18967: message/rfc822 attachments should not be base64 encoded
Issue #18967: Added regression/feature tests for encoding exceptions, made the rules only apply on message/rfc822 mime-types and not all message/* mimetypes.
Issue #18967: Documentation of new attachment behaviour for attaching emails to emails