[1.7.x] Updated doc links to point to Python 3 documentation

Backport of 680a0f08b from master.
[1.7.x] Specified 'csv and unicode' note as Python 2 only

Backport of 2128b3a6 from master.
[1.7.x] Fixed #3214 -- Stopped parsing SQL with regex.

Avoided introducing a new regex-based SQL splitter in the migrations
framework, before we're bound by backwards compatibility.

Adapted this change to the legacy "initial SQL data" feature, even
though it's already deprecated, in order to facilitate the transition
to migrations.

sqlparse becomes mandatory for RunSQL on some databases (all but
PostgreSQL). There's no API to provide a single statement and tell
Django not to attempt splitting. Since we have a more robust splitting
implementation, that seems like a good tradeoff. It's easier to add a
new keyword argument later if necessary than to remove one.

Many people contributed to both tickets, thank you all, and especially
Claude for the review.

Refs #22401.

Backport of 8b5b199 from master
[1.7.x] Fix many many typos in comments throughout the codebase

Backport of 2bcb8bfc8d from master
[1.7.x] Documented django.setup().

Thanks Eric Holscher and Tim Graham for the review.

Backport of 58ed387 from master
[1.7.x] Fixed #22526 -- Added note about check() method to 1.7 release notes.

Thanks kevin-brown for the report.

Backport of 8905fcbda6 from master
[1.7.x] Improved formatting and links of migration docs.

Backport of ab8d8e00c9 from master
[1.7.x] Fixed #22445 -- Added how to perform a reverse data migration to topic guide.

Thanks Karen Tracey for the report.

Backport of 1ce759b69f from master
[1.7.x] Fixed #22497 -- Highlighted difference between field and class deconstruction.

Thanks nliberg for the suggestion.

Backport of b829d53b37 from master
[1.7.x] Fix a typo in logging.txt

Backport of dd3f3e4e89 from master
[1.7.x] Fixed #22254 -- Noted the requirement of calling django.setup() when running

Thanks Peter Landry for the report.

Backport of 26b03f2526 from master
[1.7.x] Bump version number for 1.7 beta 3 bugfix release.
[1.7.x] Revert "Fixed #15179 -- middlewares not applied for test client login()"

This reverts commit 4fdd51b73240bf9c8d9472fcc45df699f0714755.

See the ticket for concerns with this implementation; it will be revisited.

Backport of aabceadd7d from master
[1.7.x] Added dates to release notes of today's release.

Backport of 68d264059a from master
[1.7.x] Added stub release notes for 1.6.5.

Backport of 650065f0ef from master