I made some alterations to the one zone free-fall test to allow for the option of considering pressure gradient forces in determining the rate of collapse. For this, I followed the setup described in Omukai et. al. (2005). This fixes an issue I was seeing for zero-metallicity collapse where the temperature increases rapidly at high density because collapse is continuing at the freefall rate.
This new behavior can be turned off again by setting OneZoneFreefallUseEffectiveGamma to 0, which is actually the default. This may make this test a little more useful for testing high density chemistry.
Thanks for the clarification. I don't think it's necessary to do a separate PR for enzo-3.0 since we can pull in changes from the tip of enzo-dev en masse instead of repeating pull requests over there.
I just ran this against the enzo 2.2 gold standard (transplanting just the changes in this pull request to enzo 2.2) and it passed all tests except for the OneZoneFreefallTest, which is to be expected since this change clearly improves on that one. Therefore I think we should pull this in now.