Use global thread ID instead of local one.

boards/models/post.py

@@ -237,7 +237,8 b' class PostManager(models.Manager):'
 
             if not post.is_opening():
                 thread = et.SubElement(content_tag, TAG_THREAD)
-                thread.text = str(post.get_thread().get_opening_post_id())
+                thread_id = et.SubElement(thread, TAG_ID)
+                post.get_thread().get_opening_post().global_id.to_xml_element(thread_id)
             else:
                 # TODO Output tags here
                 pass

boards/tests/test_keys.py

@@ -67,14 +67,16 b' class KeyTest(TestCase):'
                         '<id key="%s" local-id="%d" type="%s" />'
                         '<title>test_title</title>'
                         '<text>[post]%d[/post]</text>'
-                        '<thread>%d</thread>'
+                        '<thread><id key="%s" local-id="%d" type="%s" /></thread>'
                         '<pub-time>%s</pub-time>'
                         '</content>' % (
                             key.public_key,
                             reply_post.id,
                             key.key_type,
                             post.id,
+                            key.public_key,
                             post.id,
+                            key.key_type,
                             str(reply_post.get_pub_time_epoch()),
                         ) in response,
                         'Wrong XML generated for the GET response.')

docs/samples/response_get.xml

@@ -14,7 +14,7 b''
                 <id key="id1" type="ecdsa" local-id="1" />
                 <title>13</title>
                 <text>Thirteen</text>
-                <thread>id1/12</thread>
+                <thread><id key="id1" type="ecdsa" local-id="2" /></thread>
                 <pub-time>12</pub-time>
                 <!--
                     Images are saved as attachments and included in the