Update on what I found
is not based on AC 3.3 or at least it no longer is.
Left: AP_State.cpp from AC 3.3
Middle: AP_State.cpp from AC 3.4
Right: AP_State.cpp from PR
notice some differences.
You may be right that this "was" based on 3.3
It was "rebased" onto Master since May 6 2016.
"Rebase-based workflow: keeping your code up to date
As you develop, the (original) master branch of the ArduPilot repository is likely to be updated, and you should keep your fork and your local branches up to date. Rebasing allows you to re-apply your changes on top of the latest version of the original repo, making it much easier for the project to merge them."
Question is: Which version I should start with then?