[1.4.X] Fixed #18118 -- Improved documentation for contrib.auth.hashers...

[1.4.X] Fixed #18118 -- Improved documentation for contrib.auth.hashers utility functions. Thanks Mathieu Agopian for the report and Ramiro Morales for the review.

Backport of r17905 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.4.X@17906 bcc190cf-cafb-0310-a4f2-bffc1f526a37