tests/failfilemerge.py

scmutil: handle conflicting files and dirs in origbackuppath

When ui.origbackuppath is set, .orig files are stored outside of the working
copy.  However conflicts can occur when files or directories end up having the
same name.  These conflicts cause Mercurial to abort, even if they've been
created as a result of different backups.

Make sure we always replace files or directories in the origbackuppath if
they conflict with another file or directory.

Test Plan:
Add new unit test for conflicting paths.

Differential Revision: https://phab.mercurial-scm.org/D680

# extension to emulate interrupting filemerge._filemerge

from __future__ import absolute_import

from mercurial import (
    error,
    extensions,
    filemerge,
)

def failfilemerge(filemergefn,
                  premerge, repo, wctx, mynode, orig, fcd, fco, fca,
                  labels=None):
    raise error.Abort("^C")
    return filemergefn(premerge, repo, mynode, orig, fcd, fco, fca, labels)

def extsetup(ui):
    extensions.wrapfunction(filemerge, '_filemerge',
                            failfilemerge)