record: make the m key open an editor for the commit message (issue5667) With the former crecord extension, the user could edit the commit message while he was de-/selecting hunks. By pressing 'm', an editor showed up to edit the commit message. With record being part of mercurial, this feature is not available anymore. However, the help text still mentions it. As the infrastructure needed is still present, this feature is quite easily ported from the crecord extension to mercurial. It seems there is no test coverage for record ui, so I tested this patch manually on my local machine.