Gravity infrastructure

Sorry, this is a bulky one. Not all of the gravity is here but most of the infrastructure is in place. It's getting tricky to maintain this separate so I'd like to merge all the innocuous changes to the master branch. All of the gravity tasks and the logic is in place. Only the content of some of them needs to be more thoroughly checked for accuracy and I need to merge the FFT task once I am happy with it.

With this in it should be much easier for me and Bert to re-import gizmo into the master.

Could you stress test this and verify that your usual hydro test-cases still run ? I'll bring gravity test cases in at a later point.

BTW, should I git squash the commits to have a cleaner git log ?

This is a first implementation of #25 (closed) and #176 (closed).

Re: git squash, no not for this branch as it has been published and all the people with clones now have this history. Ideally you'd squash trivial commits before pushing. You could consider making a branch from gravity_infrastructure and then squashing that, before pushing, if the history is really bad...

Ah yes, too late at this stage. I can make a separate branch with a squashed version of this one if 88 commits is too much for a clean history. Let me know.

Added 10 commits:

• 87947e64...6ed86e0a - 9 commits from branch master
• bbb5dfb8 - Merge branch 'master' into gravity_infrastructure

Added 1 commit:

• 3411dd0f - Fix merge issues and FFTW include files

Found a couple of issues that I've fixed. Other than those, looks good to go for now, so accepting.

Status changed to merged

mentioned in commit ad5c2154

I'll leave the branch for you to keep or not.

Thanks for checking all this. Looks like my trick of creating a sub-branch backfired but I should be able to recover the state of my working branch as it was.