Only create one TaggedItem if the same tag is given more than once, with a test…

Only create one TaggedItem if the same tag is given more than once, with a test showing the problem.  Fixes issue #8 (http://github.com/alex/django-taggit/issues#issue/8) by applying Charlie's patch.

taggit/managers.py

@@ -127,7 +127,7 @@ class _TaggableManager(models.Manager):
         for tag in tags:
             if not isinstance(tag, Tag):
                 tag, _ = Tag.objects.get_or_create(name=tag)
-            TaggedItem.objects.create(object_id=self.object_id,
+            TaggedItem.objects.get_or_create(object_id=self.object_id,
                 content_type=ContentType.objects.get_for_model(self.model), tag=tag)
 
     @require_instance_manager

taggit/tests/__init__.py

-from taggit.tests.tests import AddTagTestCase, LookupByTagTestCase, TaggableFormTestCase, SimilarityByTagTestCase
+from taggit.tests.tests import AddTagTestCase, LookupByTagTestCase, TaggableFormTestCase, SimilarityByTagTestCase, TagReuseTestCase

taggit/tests/tests.py

@@ -104,3 +104,9 @@ class SimilarityByTagTestCase(BaseTaggingTest):
         similar_objs = apple.tags.similar_objects()
         self.assertEqual(similar_objs, [pear, watermelon])
         self.assertEqual(map(lambda x: x.similar_tags, similar_objs), [3, 2])
+
+class TagReuseTestCase(BaseTaggingTest):
+    def test_tag_reuse(self):
+        apple = Food.objects.create(name="apple")
+        apple.tags.add("juicy", "juicy")
+        self.assert_tags_equal(apple.tags.all(), ['juicy'])