Add experimental wrappers around YAML 1.2 tags code

This way people can play with it, and we don't promise this wrapper will stay
around forever, and newly created classes CommonDumper/CommonRepresenter aren't
exposed.

    MyCoreLoader = yaml.experimental_12_Core_loader()
    data = yaml.load(input, Loader=MyCoreLoader)

    MyCoreDumper = yaml.experimental_12_Core_dumper()
    out = yaml.dump(data, Dumper=MyCoreDumper)

lib/yaml/__init__.py

@@ -344,7 +344,17 @@ def add_multi_representer(data_type, multi_representer, Dumper=Dumper):
     """
     Dumper.add_multi_representer(data_type, multi_representer)
 
+def experimental_12_Core_loader():
+    return loader._12_CoreLoader
+def experimental_12_JSON_loader():
+    return loader._12_JSONLoader
+
+def experimental_12_Core_dumper():
+    return dumper._12_CoreDumper
+def experimental_12_JSON_dumper():
+    return dumper._12_JSONDumper
 class YAMLObjectMetaclass(type):
+
     """
     The metaclass for YAMLObject.
     """

lib/yaml/dumper.py

@@ -83,3 +83,8 @@ def __init__(self, stream,
                 default_flow_style=default_flow_style, sort_keys=sort_keys)
         Resolver.__init__(self)
 
+class _12_CoreDumper(CommonDumper): pass
+_12_CoreDumper.init_tags('core')
+class _12_JSONDumper(CommonDumper): pass
+_12_JSONDumper.init_tags('json')
+

lib/yaml/loader.py

@@ -67,3 +67,9 @@ def __init__(self, stream):
         Composer.__init__(self)
         Constructor.__init__(self)
         Resolver.__init__(self)
+
+class _12_CoreLoader(BaseLoader): pass
+_12_CoreLoader.init_tags('core')
+class _12_JSONLoader(BaseLoader): pass
+_12_JSONLoader.init_tags('json')
+