[1.6.x] Fixed #21662 -- Kept parent reference in prepared geometry

Thanks Robert Scott for the report.
Backport of 542198c1d0 from master.
[1.6.x] Fixed #21627 -- Added unicode_literals to changepassword command.

Fixed a crash when executing changepassword command when the user object
representation contained non-ASCII characters.

Backport of 398642fd9b from master
[1.6.x] Fixed typo and slightly improved error message when db is missing time zone definitions.

Refs #21432.

Backport of 32e75803be from master
[1.6.x] Fixed #21629 -- Added instructions for loading MySQL time zone definitions.

Thanks Aymeric for the suggestion.

Backport of d8d83777eb from master
[1.6.x] Fixed #21582 -- Corrected URL namespace example.

Thanks oubiga for the report.

Backport of 025ec2e7fe from master