Added more tests and documentation for dictsort.

It's possible to use something like {{ foo|dictsort:'bar.baz' }}
but this wasn't tested or documented.

docs/ref/templates/builtins.txt

@@ -1433,6 +1433,27 @@ then the output would be:
         {'name': 'zed', 'age': 19},
     ]
 
+You can also do more complicated things like::
+    {{ for book in books|dictsort:"author.age"
+        * {{ book.title }} ({{ book.author.name }})
+    {% endfor %}
+
+If ``books`` is:
+
+.. code-block:: python
+
+    [
+        {'title': '1984', 'author': {'name': 'George', 'age': 45}},
+        {'title': 'Timequake', 'author': {'name': 'Kurt', 'age': 75}},
+        {'title': 'Alice', 'author': {'name': 'Lewis', 'age': 33}},
+    ]
+
+the the output would be::
+
+    * Alice (Lewis)
+    * 1984 (George)
+    * Timequake (Kurt)
+
 .. templatefilter:: dictsortreversed
 
 dictsortreversed

tests/defaultfilters/tests.py

@@ -441,6 +441,20 @@ class DefaultFiltersTests(TestCase):
         self.assertEqual(dictsort({'a': 1}, 'age'), '')
         self.assertEqual(dictsort(1, 'age'), '')
 
+    def test_dictsort_complex_sorting_key(self):
+        """
+        Since dictsort uses template.Variable under the hood, it can sort
+        on keys like 'foo.bar'.
+        """
+        data = [
+            {'foo': {'bar': 1, 'baz': 'c'}},
+            {'foo': {'bar': 2, 'baz': 'b'}},
+            {'foo': {'bar': 3, 'baz': 'a'}},
+        ]
+        sorted_data = dictsort(data, 'foo.baz')
+
+        self.assertEqual([d['foo']['bar'] for d in sorted_data], [3, 2, 1])
+
     def test_dictsortreversed(self):
         sorted_dicts = dictsortreversed([{'age': 23, 'name': 'Barbara-Ann'},
                                          {'age': 63, 'name': 'Ra Ra Rasputin'},