evolve: pin the public cset to local side in merging when solving public div
While working on public divergence, I think it would be better to pin
the public cset to local side of merge for understanding and handling
the future cases without any ambiguity.
Changes in tests reflect the changed behaviour.
evolve: add tests of relocation case in public divergence
These tests cover the cases when "other" is behind the "public"
one and we would have to relocate "other" here. It covers
all the conflicting and non-conflicting cases.