dispatch: set descriptors on the request repo.ui

dispatch: pass the correct ui to runcommand For commands that take a repo, repo.ui is passed as the ui to runcommand. This restores that behaviour when the request has a repo.

archive: wrap the ui descriptor so it doesn't get closed archival.tarit closes the fileobj if one is passed to it, which is undesired when reading from '-'.

transplant: use ui out descriptor when calling util.system