Added another test to confirm fix in r16663.

This is the test case from #6045, which was fixed by the above commit.
Refs #6045, #16299

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16679 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/modeltests/m2m_and_m2o/models.py

@@ -19,3 +19,7 @@ class Issue(models.Model):
 
     class Meta:
         ordering = ('num',)
+
+class UnicodeReferenceModel(models.Model): 
+    others = models.ManyToManyField(u"UnicodeReferenceModel") 
+

tests/modeltests/m2m_and_m2o/tests.py

@@ -1,7 +1,7 @@
 from django.db.models import Q
 from django.test import TestCase
 
-from models import Issue, User
+from models import Issue, User, UnicodeReferenceModel
 
 
 class RelatedObjectTests(TestCase):
@@ -73,3 +73,16 @@ class RelatedObjectTests(TestCase):
             ],
             lambda i: i.num
         )
+
+class RelatedObjectTests(TestCase): 
+    def test_m2m_with_unicode_reference(self): 
+        """
+        Regression test for #6045: references to other models can be unicode
+        strings, providing they are directly convertible to ASCII.
+        """
+        m1=UnicodeReferenceModel.objects.create() 
+        m2=UnicodeReferenceModel.objects.create() 
+        m2.others.add(m1) # used to cause an error (see ticket #6045) 
+        m2.save() 
+        list(m2.others.all()) # Force retrieval.
+