[1.7.x] Fixed #22881 -- Better soft_applied migration detection
[1.7.x] Fixed #8033 -- Explained app registry error during translation setup

Thanks Tim Graham and Aymeric Augustin for the review.
Backport of 9618d68b34 from master.
[1.7.x] Cleaned temp dir in symlinks_supported()

Refs #21482.
Backport of 18b3788401 from master.
[1.7.x] Ensured cache tests do not leak temp dirs

Refs #17215.
Backport of 1d9596025e from master.
[1.7.x] Created import-time test temp dirs in known location

Refs #17215. In the same spirit as 5de31cb8cb.
Backport of 809362518d from master.
[1.7.x] Fixed #22888 -- Removed some unnecessary text in tutorial 3.

Backport of 1bbffe7867 from master
[1.7.x] Fixed test failures introduced by refs #22881.

Backport of 908160f692 from master
[1.7.x] Removed 'to_field' from ForeignKey(settings.AUTH_USER_MODEL) in admin's initial migration.

This enables using a custom user model with a primary key with a name
different than 'id'; refs #22889.

Backport of bcd2e6c697 from master