Began converting localflavor doctests into unittests, starting with the German...

Began converting localflavor doctests into unittests, starting with the German ones.  Also introduced a new base class to facilitate ease of testing form fields. We have always been at war with doctests.  Thanks to Idan Gazit for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14626 bcc190cf-cafb-0310-a4f2-bffc1f526a37