changeset_templater: only compute manifest when --debug.
%%% should show a removed and b addedA bR areverting...%%% should show b unknown and a back to normal? bmerging a%%% should show foo-bfoo-b%%% should show a removed and b addedA bR areverting...%%% should show b unknown and a marked modified (merged)? b%%% should show foo-bfoo-b