enhancement request: make py3 read/write py2 pickle format

[Serhiy Storchaka]

On 09.06.15 21:31, Laura Creighton wrote:
> We have an issue about that.
> https://bugs.python.org/issue13566
>
> Go there and say you want it too. :)

I afraid issue title is too general. :) The issue is only about one 
minor detail of py3 to py2 compatibility.