tests/crashgetbundler.py

filemerge: use arbitraryfilectx for backups

 With in-memory merge, backup files might be overlayworkingfilectxs stored
in memory. But they could also be real files if the user's backup directory is
outside the working dir.

Rather than have two code paths everywhere, let's use arbitraryfilectx so they
can be consistent.

Differential Revision: https://phab.mercurial-scm.org/D1057

from __future__ import absolute_import

from mercurial.i18n import _
from mercurial import (
        changegroup,
        error,
        extensions
    )

def abort(orig, *args, **kwargs):
    raise error.Abort(_('this is an exercise'))

def uisetup(ui):
    extensions.wrapfunction(changegroup, 'getbundler', abort)