cmdrewrite: a new `hg fixup` command

This new command can be used to amend changes to a specific revision.

Implementation wise what it basically does is:

1) commit the working directory changes
2) relocate the new commit onto the target commit
3) fold them into one.

After the run, the working directory parent will be the obsoleted
changeset created in step(1) and descendants of the target will
get orphan instability.
9 jobs for topic/default/cmd-fixup in 13 minutes and 47 seconds (queued for 2 seconds)
Name Stage Failure
failed
windows-py3 Test There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job log