[1.1.X] Fixed a few more spots related to #11859. Backport of r12537 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12538 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/fields/__init__.py

@@ -304,7 +304,7 @@ class Field(object):
         """Flattened version of choices tuple."""
         flat = []
         for choice, value in self.choices:
-            if type(value) in (list, tuple):
+            if isinstance(value, (list, tuple)):
                 flat.extend(value)
             else:
                 flat.append((choice,value))

django/forms/fields.py

@@ -660,7 +660,7 @@ class ChoiceField(Field):
     def valid_value(self, value):
         "Check to see if the provided value is a valid choice"
         for k, v in self.choices:
-            if type(v) in (tuple, list):
+            if isinstance(v, (list, tuple)):
                 # This is an optgroup, so look inside the group for options
                 for k2, v2 in v:
                     if value == smart_unicode(k2):