Similar to issue4009, 2.7 will force people to abort histedits before
doing interesting things. Without this fix, people with histedit
sessions they wandered away from before upgrading to 2.7 could clobber
their working copy for no reason.
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.
