Merges commits and tries to resolve any conflicts recursively.
Merges commits without attempting to resolve file conflicts.
Moves target_commits from their current location to a new location in the
graph, given by the set of new_parent_ids and new_children.
The roots of target_commits are rebased onto the new parents, while the
new children are rebased onto the heads of target_commits.
This assumes that target_commits and new_children can be rewritten, and
there will be no cycles in the resulting graph.
target_commits should be in reverse topological order.
Moves changes from sources to the destination parent, returns new tree.
Restore matching paths from the source into the destination.