Towards a solution for sphinx-doc/sphinx#1704.

Elements now get multiple ids to keep permalinks permanent. The default
id is the newest style, which is used as the shown permalink and in the
index. The old style ids have been (partially) replicated and are
temporarily used as the default id for testing purposes.

tests/test_domain_cpp.py

@@ -39,7 +39,8 @@ def check(name, input, output=None):
     ast.describe_signature([], 'lastIsName', None)
     ast.prefixedName = ast.name  # otherwise the get_id fails, it would be set
                                  # in handle_signarue
-    ast.get_id()
+    ast.get_id_v1()
+    ast.get_id_v2()
     #print ".. %s:: %s" % (name, input)
 
 def test_type_definitions():