Modern versions of Django provide new password hashers, and deprecate

legacy ones. Some of those deprecated ones are still used in production,

so we can't get rid of them just yet. This change sets a list of all the

hashers we know we'll want to use.
Note that Django will only use the first one for creating new hashes,

but will support passwords made in all following hashers.

Unit tests pass on Django 1.6 and 1.11.