scm: select options should be tuples - not lists with 2 elements We use tuples in all(?) other places, so we should do the same here. Since lists can be unpacked as tuples, it currently works to use 2-lists. But in a following change for "correct" handling of webhelpers.select when using webhelpers2.select, we want to give special handling to tuples vs strings vs Options. We don't want to add list to that list.

# requirements.txt file for use as "pip install -r requirements.txt" as a
# readthedocs compatible alternative to "pip install -e ." which is a working
# alternative to "setup.py develop" which doesn't work with Mercurial 3.7
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