[1.7.x] Fixed #22539 -- Copied exclude argument in Model.full_clean() to prevent side effects.

Backport of e2e4cdba11 from master
[1.7.x] Fixed #22551 -- Made oracle backend method Python 3 compatible

Thanks fatal10110 at gmail.com for the report. The fix is 1.6-only
because that code has been refactored in 1.7 (6983201cfb).
'Docs-only' forward port of 120a98120 from 1.6.x.
[1.7.x] Fix migration autodector to work correctly with custom deconstructed values
[1.7.x] Fixed #22558 -- Added missing word in contributing docs

Backport of c8d257e81 from master.
[1.7.x] Fixed #22565 -- Prevented pgettext_lazy crash with bytestring input

Thanks ygbo for the report.
Backport of 142c27218 from master.