Don't assume auto-handle; don't send self-remove

[bifurcation]

The current script generator makes two assumptions that are not necessarily true:

1. That a client automatically cues any proposals that it creates for commit, and thus doesn't need to be instructed to commit them
2. That a client can gracefully handle a commit that removes the client

This PR makes the corresponding changes to scenario generation to accommodate the case where these are not true:

1. All proposals are explicitly signaled in byReference, including those created by the committer
2. A commit that removes a member is not sent to that member