Make weak references subclassable:

- weakref.ref and weakref.ReferenceType will become aliases for each
  other

- weakref.ref will be a modern, new-style class with proper __new__
  and __init__ methods

- weakref.WeakValueDictionary will have a lighter memory footprint,
  using a new weakref.ref subclass to associate the key with the
  value, allowing us to have only a single object of overhead for each
  dictionary entry (currently, there are 3 objects of overhead per
  entry: a weakref to the value, a weakref to the dictionary, and a
  function object used as a weakref callback; the weakref to the
  dictionary could be avoided without this change)

- a new macro, PyWeakref_CheckRefExact(), will be added

- PyWeakref_CheckRef() will check for subclasses of weakref.ref

This closes SF patch #983019.

Modules/_weakref.c

@@ -57,26 +57,6 @@ weakref_getweakrefs(PyObject *self, PyObject *object)
 }
 
 
-PyDoc_STRVAR(weakref_ref__doc__,
-"ref(object[, callback]) -- create a weak reference to 'object';\n"
-"when 'object' is finalized, 'callback' will be called and passed\n"
-"a reference to the weak reference object when 'object' is about\n"
-"to be finalized.");
-
-static PyObject *
-weakref_ref(PyObject *self, PyObject *args)
-{
-    PyObject *object;
-    PyObject *callback = NULL;
-    PyObject *result = NULL;
-
-    if (PyArg_UnpackTuple(args, "ref", 1, 2, &object, &callback)) {
-        result = PyWeakref_NewRef(object, callback);
-    }
-    return result;
-}
-
-
 PyDoc_STRVAR(weakref_proxy__doc__,
 "proxy(object[, callback]) -- create a proxy object that weakly\n"
 "references 'object'.  'callback', if given, is called with a\n"
@@ -104,8 +84,6 @@ weakref_functions[] =  {
      weakref_getweakrefs__doc__},
     {"proxy",           weakref_proxy,                  METH_VARARGS,
      weakref_proxy__doc__},
-    {"ref",             weakref_ref,                    METH_VARARGS,
-     weakref_ref__doc__},
     {NULL, NULL, 0, NULL}
 };
 
@@ -119,6 +97,9 @@ init_weakref(void)
                        "Weak-reference support module.");
     if (m != NULL) {
         Py_INCREF(&_PyWeakref_RefType);
+        PyModule_AddObject(m, "ref",
+                           (PyObject *) &_PyWeakref_RefType);
+        Py_INCREF(&_PyWeakref_RefType);
         PyModule_AddObject(m, "ReferenceType",
                            (PyObject *) &_PyWeakref_RefType);
         Py_INCREF(&_PyWeakref_ProxyType);