tests: add more tests related to stabilization of orphaned merge commit This patch more tests related to stabilization of orphaned merge commit. Stabilization of a merge changeset with both the parents is not supported right now and prints a message on how to do that. Maybe we should do that internally as a part of `hg evolve` but I need to think about this.

test-drop.t
test-inhibit.t
test-simple4server.t
tests/test-simple4server-bundle2.t