copies: remove _checkcopies wrapper - it does no good mergecopies might be doomed but it is not dead yet ...

transplant: use context ancestor instead of changelog ancestor We want to move in this direction. ctx.ancestor is in a better position for handling a situation with multiple ancestors.

commit: use revlog.commonancestors instead of .ancestor This do probably not make any real difference but is slightly more correct and we would like to get rid of flog.ancestor.

backout: don't limit heritage check to a single ancestor This do probably not make any real difference but is slightly more correct and we would like to get rid of changelog.ancestor.