scmutil.cleanupnodes is used by rebase, histedit and amend to do create
obsmarkers or strip nodes. This patch adds functionality to cleanupnodes to take
a formatter and if a formatter is passed, it will show the hash changes also.
The formatter is a optional argument, so if a command needs to show the hash
changes it can pass a formatter and if not, things work.
Some typos in the comment. Is this what you meant?
or was this a question for the reviewers?