[1.2.X] Fixed #14871, #14872 -- ZAIDField didn't handle alll EMPTY_VALUES...

[1.2.X] Fixed #14871, #14872 -- ZAIDField didn't handle alll EMPTY_VALUES correctly and ZAPostCodeField didn't respect *args or **kwargs (such as required=False).  Also converted South African localflavor doctests into unittests.  We have always been at war with doctests.  Thanks to Idan Gazit.  Backport of [14956].

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14980 bcc190cf-cafb-0310-a4f2-bffc1f526a37