[1.7.x] Fixed #23043: alter_field drops defaults too
[1.7.x] Fixed #23039: Don't try to serialize unmanaged models in tests
[1.7.x] Fixed #22975: Don't call rename SQL if not needed
[1.7.x] Fixed #23009: Shorten FK identifiers in add_field and make consistent
[1.7.x] Fixed #23014: Renaming not atomic with unique together
[1.7.x] Fixed #23064 -- Added lib detection support for GDAL 1.10/1.11

Note that GDAL 1.11 is not yet officially supported, until someone
has tested it and can confirm it has no issues with Django.
Backport of 3f1412ff7b from master.
[1.7.x] Replaced instances of 'his/her' with 'their'.

Backport of 8fbf13a6c8 from master