Code review comment for lp:~vanvugt/mir/async-is-not-sync

I think we should incentivise clients to use the async version.. and make clear which calls might include round-trips to the server. So I have a weak preference of the current state - async being the shorter version and "_sync" kind of standing out.

I think it would be more helpful to hand out an fd to make the toolkits or clients gain control over the dispatch.