graph: don't try to get obsolete status for fake parent revisions Fake parents use negative revision numbers as internal placeholders. Previous Mercurial versions could handle negative non-existing revision numbers, but Mercurial 4.8 will fail on this invalid input when getting the obsolete status. Instead, make sure we only get obsolete status for actual revisions.

# 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
.