Fixed #8210 and #8664: moved `USStateField` and `PhoneNumberField` to `django.contrib.localflavor.us`. This is a backwards-incompatible change, albeit a minor one; just add an aditional `import` and go on your way.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@8819 bcc190cf-cafb-0310-a4f2-bffc1f526a37