Issue #4072: Restore build_py_2to3. Add a distutils demo for

build_py_2to3.

Demo/distutils/test2to3/README

@@ -0,0 +1,3 @@
+This project demonstrates how a distutils package
+can support Python 2.x and Python 3.x from a single
+source, using lib2to3.

Demo/distutils/test2to3/setup.py

@@ -0,0 +1,18 @@
+# -*- coding: iso-8859-1 -*-
+from distutils.core import setup
+
+try:
+    from distutils.command.build_py import build_py_2to3 as build_py
+except ImportError:
+    from distutils.command.build_py import build_py
+
+setup(
+    name = "test2to3",
+    version = "1.0",
+    description = "2to3 distutils test package",
+    author = "Martin v. Löwis",
+    author_email = "python-dev@python.org",
+    license = "PSF license",
+    packages = ["test2to3"],
+    cmdclass = {'build_py':build_py}
+)

Demo/distutils/test2to3/test2to3/__init__.py

@@ -0,0 +1 @@
+# empty

Demo/distutils/test2to3/test2to3/hello.py

@@ -0,0 +1,5 @@
+def hello():
+    try:
+        print "Hello, world"
+    except IOError, e:
+        print e.errno