[1.5.X] Fixed #19348 - Clarified the units of filesizeformat.

Thanks george_edison for the report and Claude Paroz for the patch.

Backport of 63e6cd1bb3 from master
[1.5.X] Changed if statement to a slightly cleaner variant

Backport of eabb44417c from master
[1.5.x] Fixed #19152 -- Allowed PostGIS tests to be run without template

From version 2, a PostGIS template is no longer required to create
a GIS-enabled database.
Backport of fbd1df8e from master.
[1.5.x] Fixed cursor commit command in PostGIS backend

Thanks Bruno Renié for noticing the error.
Backport of 7b9a1fb96 from master.
[1.5.x] Fixed #18375 -- Removed dict-ordering dependency for F-expressions

F() expressions reuse joins like any lookup in a .filter() call -
reuse multijoins generated in the same .filter() call else generate
new joins. Also, lookups can now reuse joins generated by F().

This change is backwards incompatible, but it is required to prevent
dict randomization from generating different queries depending on
.filter() kwarg ordering. The new way is also more consistent in how
joins are reused.

Backpatch of 90b86291d022a09031d1df397d7aaebc30e435f7
[1.5.x] Negligible style fix in docs.

Backport of 5c81e9d.
Added new languages

Afrikaans, Belarusian, Breton, Venezuelan Spanish, Interlingua,
Luxembourgish, Udmurt
[1.5.x] Fixed SQLite's collapsing of same-valued instances in bulk_create

SQLite used INSERT INTO tbl SELECT %s UNION SELECT %s, the problem
was that there should have been UNION ALL instead of UNION.

Refs #19351

Backpatch of a27582484cf814554907d2d1ad077852de36963f
[1.5.x] Fixed #19351 -- SQLite bulk_insert of more than 500 single-field objs

Backpatch of 0a0a0d66b316598f7c296e8bf75749a14ce3ac49
Changed Luxembourgish name_local to unicode escapes.

Fixes 6a00c196.
[1.5.x] Fixed #19806 -- Ensure that content types and permissions aren't created for swapped models.

Thanks to rizumu for the report.

Backport of c8985a8a7317042a641e870cb75b3005cc5d67b1.
[1.5.x] Fixed #19218 -- Added documentation note on limitations of signals with custom User models.

Thanks to kunitoki@gmail.com for the report.

Backport of fdb5c98d7ee54c7f89ec10b0203263f1f5b37510.
[1.5.x] Simplified the deletions performed by the swappable_models test.

This is required to allow the test to run without error under SQLite in the CI environment.

Backport of 18d7c1e.
[1.5.x] Removed some stray debug lines introduced accidentally in c8985a8.

Backport of f2d8004.
[1.5.x] Fixed #19343 -- Deadlock with TransactionTestCase + TEST_MIRROR + multi_db.

Thanks Jeremy Dunck for the review.

Backport of be64dd3 from master.
[1.5.x] Fixed #19237 -- Improved strip_tags utility

The previous pattern didn't properly addressed cases where '>'
was present inside quoted tag content.
Backport of bf1871d87 from master.
[1.5.x] Fixed ordering-related failure in m2m_through_regress tests

Backpatch of dc569c880143db07e01b3293d698ad8fe4a0136f
[1.5.x] Updated User manager when testing custom AUTH_USER_MODEL

This is giving more real test conditions when AUTH_USER_MODEL is
set with override_settings.
Backport of a962bc7c4 from master.
[1.5.x] Fixed #18722 -- Adjusted width of sortable columns in admin

Thanks Simon Charette for the report.
Backport of 35a0fff2 from master.
[1.5.x] Fixed #19293 -- Updated Czech input formats

Thanks vzima for the report.
Backport of abd0e76d2 from master.