[1.7.x] Fixed #21084 -- Used proxy model's content type for admin log entries.

Backport of 7a7f6fccae from master
[1.7.x] Fixed #21084 -- Used proxy model's content type for admin log entries.

(the previous commit included only the test)

Backport of 3cba90f22a from master
[1.7.x] Added missing request parameter to get_current_site().

Backport of d6c9bdd825 from master