merge: fix --preview to show all nodes that will be merged (
issue2043).
Formerly, it omitted nodes that were not descendants of the least
common ancestor of the two merge parents, even though those nodes
contribute to the merge. The new algorithm uses revlog.findmissing()
instead of ancestor() + nodesbetween().
adding changeset.txt
adding mymap
0 97e5f848f0936960273bbf75be6388cd0350a32b test