The previous version of Argon2 uses encoded hashes of the form:
   $argon2d$m=8,t=1,p=1$<salt>$<data>

The new version of Argon2 adds its version into the hash:
   $argon2d$v=19$m=8,t=1,p=1$<salt>$<data>

This lets Django handle both version properly.

Unused since afe0bb7b.

Thanks Anders Roos for the report.

The test sometimes fails on CI and isn't worth debugging at this time.

Unused since afe0bb7b.

Thanks for Simon Willison for the spot.

Unused since its introduction in dc334a2b.

Adds a reasonably feature complete implementation of full text search
using the built in PostgreSQL engine. It uses public APIs from
Expression and Lookup.

With thanks to Tim Graham, Simon Charettes, Josh Smeaton, Mikey Ariel
and many others for their advice and review. Particular thanks also go
to the supporters of the contrib.postgres kickstarter.

Thanks Tim Graham for the review.

For example, this avoids a warning in the case of a request that's
redirected to a language-prefixed URL by LocaleMiddleware.

Fixed #26281 -- Added a helpful error message for an invalid format specifier to dateformat.format().

The latest version (16.1) is backwards-incompatible for Django.

Thanks NotSqrt for the excellent report and Tim Graham for the review.