rebase: accept multiple --base arguments (BC)
Same reasoning as for the previous patch. Rebase has worked well with
`--base 'A + B'` since 51e7c83e05ee (rebase: calculate ancestors for
--base separately (issue5420), 2016-11-28).
Differential Revision: https://phab.mercurial-scm.org/D8293
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true