[py3] Ported django.utils.encoding.

* Renamed smart_unicode to smart_text (but kept the old name under
  Python 2 for backwards compatibility).
* Renamed smart_str to smart_bytes.
* Re-introduced smart_str as an alias for smart_text under Python 3
  and smart_bytes under Python 2 (which is backwards compatible).
  Thus smart_str always returns a str objects.
* Used the new smart_str in a few places where both Python 2 and 3
  want a str.

django/db/models/fields/files.py

@@ -8,7 +8,7 @@ from django.core.files.base import File
 from django.core.files.storage import default_storage
 from django.core.files.images import ImageFile
 from django.db.models import signals
-from django.utils.encoding import force_unicode, smart_str
+from django.utils.encoding import force_text, smart_bytes
 from django.utils import six
 from django.utils.translation import ugettext_lazy as _
 
@@ -280,7 +280,7 @@ class FileField(Field):
         setattr(cls, self.name, self.descriptor_class(self))
 
     def get_directory_name(self):
-        return os.path.normpath(force_unicode(datetime.datetime.now().strftime(smart_str(self.upload_to))))
+        return os.path.normpath(force_text(datetime.datetime.now().strftime(smart_bytes(self.upload_to))))
 
     def get_filename(self, filename):
         return os.path.normpath(self.storage.get_valid_name(os.path.basename(filename)))