Adding crc32 to uniqueify conversation URIs

This really should be a UUID or something else totally unexpected
but I figure that crc32 is good enough for now. The reason we keep
the main structure is because some third party scripts have begun
relying upon the tag URI format to parse out domain name, type etc.

classes/Conversation.php

@@ -71,10 +71,11 @@ class Conversation extends Managed_DataObject
         $conv = new Conversation();
         $conv->created = common_sql_now();
         $conv->id = $notice->id;
-        $conv->uri = $uri ?: sprintf('%s%s=%d:%s=%s',
+        $conv->uri = $uri ?: sprintf('%s%s=%d:%s=%s:%s=%x',
                              TagURI::mint(),
                              'noticeId', $notice->id,
-                             'objectType', 'thread');
+                             'objectType', 'thread',
+                             'crc32', crc32($notice->content));
         $result = $conv->insert();
 
         if ($result === false) {