sshserver: flush stream after command dispatch I am not sure why this is not working as expected, but without this client might not see some important output. Without this patch moving some output at transaction closing time makes it disapear for ssh client in various sitaution.

narrow: rely on setting `quiet` mode instead of `pushbuffer` The `quiet` approach is what `shelve` uses and give the same result. This will help us to add less code in future changesets.