Restack tracking issue

[9999years]

restack works at least mostly but needs a bunch of fixes. Let's track them all here.

• Do not restack abandoned changes #48
• Restore the previously checked out change after restacking #44
• Unify restack this and restack #36
• Cope with the user running git cherry-pick --continue before git gr restack continue #35
• Restack: Use rebase instead of cherry-pick #49
• Restack: Show out-of-date changes #33
• Restack: Show steps before starting work #34