content-div: add test showing `--stop` works during interrupted resolution This patch adds a test showing that the --stop flag of `hg evolve` works well during interrupted content-divergence resolution. The --stop flag now works with all the three different type of instability resolution very well and we should advertise it more.

evolve: create new commit while resolving content-divergence Before this patch, we used to amend one of the content-divergent changes with the changes from the merge. Creating a new commit will certain advantages like letting user enter a commit message, showing user the new merge diff before commiting the content-divergent resolution and give us more control in the implementation part. The reason amend was used initially was just because it was easy. There are some tests update due to change.