[petsc-dev] futurize

[Jed Brown]

Would it be too disruptive to run futurize "stage 1" before the 3.9
release?  The source would remain Python-2 only, but would be
"modernized" so that the next stage (supporting Python-3) would be less
disruptive.  The goal here would be to make it easier to port
configuration changes from 'maint' to 'master' after the release, under
the assumption that we'll want to support Python-3 before a 3.10
release.