[PATCH 1 of 8] bdiff: add _version to help detect breaking binary changes

[Jun Wu]

Excerpts from Yuya Nishihara's message of 2017-05-03 11:02:18 +0900:
> On Tue, 2 May 2017 18:33:50 -0700, Jun Wu wrote:
> > The problem we faced for issue4042 fix is to maintain compatibility in both
> > directions without copy-paste.
> > 
> > The "_duralmodule" approach is while smart, does not really solve the above
> > problem. i.e. copy-paste is still needed.
> 
> No. We can just rename fix_newline() to fixnewline2(). New code has
> pure.diffhelpers.fixnewline2() as a fallback, and old one does
> pure.diffhelpers.fix_newline(). That's how we solved API changes
> historically.

The problem is that only works with non-default modulepolicy.