[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/sql/query.py

@@ -10,7 +10,7 @@ all about the internals of models in order to get the information it needs.
 import copy
 
 from django.utils.datastructures import SortedDict
-from django.utils.encoding import force_unicode
+from django.utils.encoding import force_text
 from django.utils.tree import Node
 from django.utils import six
 from django.db import connections, DEFAULT_DB_ALIAS
@@ -1776,7 +1776,7 @@ class Query(object):
             else:
                 param_iter = iter([])
             for name, entry in select.items():
-                entry = force_unicode(entry)
+                entry = force_text(entry)
                 entry_params = []
                 pos = entry.find("%s")
                 while pos != -1: