test-histedit: reorder phases test and prepare for more We are going to add a lot regarding phase of test while fixing issue3724. This movement allows to put them after this first phase test.

test-histedit: fix instability creation test The current test does not rewrite anything and therefor does not create any instability. We also clean up the repo state after the test. This required the rebase extension.

histedit: record histedit source (issue3681) Have histedit record the hex of the original changeset as already done by: - graft - commit --amend - rebase My main motivation for adding this is to prevent the creation of obsolescence cycle (see issue3681). Note that commit created during edit are not affected yet.

histedit: factor most commit creation in a function Later commits add two important items to histedit: - Obsolescence cycle prevention - Proper phase conservation Those logics must be applied to all simple operations (pick, edit, mess) and will require verbose code. So we introduce a new function that will provide an entry point for this new. logic. The function build a closure to have a clear distinction between commit arguments and data provided to the function to fulfil its logic.