ok millert

ok tracey

this is for got push and got fetch, primarily ok stsp

semarie@ reported an error from go-git used by Cirrus CI: "57243613255d758e15b0f5ae1c960b970f0435f8: malformed mode (0100640)!" 'git fsck' has no problem with mode 0100640. But writing just the two most commonly used file modes should provide the best compatibility.

Commit IDs on histedit's temporary branch can change arbitrarily because the user may create new commits on this branch while editing past commits. So there is no point in trying to verify these IDs like we do during rebase. Add a test case which demonstrates the problem.