merge: add a 'keepconflictparent' argument to graft Before this change, `merge.graft` was always dropping the "grafted" changeset from the parent. This is impractical in case of conflict as the second parent can be useful to help with conflict resolution. We add a new boolean parameter to control this behavior. This will make using `merge.graft` directly in shelve practicable. Differential Revision: https://phab.mercurial-scm.org/D3692