git_remote_helpers: use 2to3 if building with Python 3

Using the approach detailed in the Python documentation[1], run 2to3 on
the code as part of the build if building with Python 3.

The code itself requires no changes to convert cleanly.

[1] http://docs.python.org/3.3/howto/pyporting.html#during-installation

Signed-off-by: John Keeping <john@keeping.me.uk>
Acked-by: Sverre Rabbelier <srabbelier@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git_remote_helpers/setup.py

@@ -4,6 +4,15 @@
 
 from distutils.core import setup
 
+# If building under Python3 we need to run 2to3 on the code, do this by
+# trying to import distutils' 2to3 builder, which is only available in
+# Python3.
+try:
+    from distutils.command.build_py import build_py_2to3 as build_py
+except ImportError:
+    # 2.x
+    from distutils.command.build_py import build_py
+
 setup(
     name = 'git_remote_helpers',
     version = '0.1.0',
@@ -14,4 +23,5 @@ setup(
     url = 'http://www.git-scm.com/',
     package_dir = {'git_remote_helpers': ''},
     packages = ['git_remote_helpers', 'git_remote_helpers.git'],
+    cmdclass = {'build_py': build_py},
 )