Enable GC for new-style instances. This touches lots of files, since

many types were subclassable but had a xxx_dealloc function that
called PyObject_DEL(self) directly instead of deferring to
self->ob_type->tp_free(self).  It is permissible to set tp_free in the
type object directly to _PyObject_Del, for non-GC types, or to
_PyObject_GC_Del, for GC types.  Still, PyObject_DEL was a tad faster,
so I'm fearing that our pystone rating is going down again.  I'm not
sure if doing something like

void xxx_dealloc(PyObject *self)
{
	if (PyXxxCheckExact(self))
		PyObject_DEL(self);
	else
		self->ob_type->tp_free(self);
}

is any faster than always calling the else branch, so I haven't
attempted that -- however those types whose own dealloc is fancier
(int, float, unicode) do use this pattern.

Lib/test/test_gc.py

@@ -73,6 +73,24 @@ def test_instance():
     del a
     expect_nonzero(gc.collect(), "instance")
 
+def test_newinstance():
+    class A(object):
+        pass
+    a = A()
+    a.a = a
+    gc.collect()
+    del a
+    expect_nonzero(gc.collect(), "newinstance")
+    class B(list):
+        pass
+    class C(B, A):
+        pass
+    a = C()
+    a.a = a
+    gc.collect()
+    del a
+    expect_nonzero(gc.collect(), "newinstance(2)")
+
 def test_method():
     # Tricky: self.__init__ is a bound method, it references the instance.
     class A:
@@ -170,6 +188,7 @@ def test_all():
     run_test("static classes", test_staticclass)
     run_test("dynamic classes", test_dynamicclass)
     run_test("instances", test_instance)
+    run_test("new instances", test_newinstance)
     run_test("methods", test_method)
     run_test("functions", test_function)
     run_test("frames", test_frame)