py3: use bytes in place of basestring
All strings in mercurial must be bytes so we can easily replace basestring with
bytes.
Differential Revision: https://phab.mercurial-scm.org/D1555
Martin von Zweigbergk <martinvonz@google.com> [Fri, 01 Dec 2017 14:13:55 -0800] rev 35196
amend: make a copy of "extra" to avoid mutating an input
I don't know of any problems this has caused, it just seems less
surprising.
Differential Revision: https://phab.mercurial-scm.org/D1575