When we change a stream name, we now use the stream id as the
key to find messages we need to live update. This eliminates
some possible race conditions from two users renaming a stream.
This commit introduces message_live_update.js.
The new call stack is this:
subs.update_subscription_properties
subs.update_stream_name
message_live_update.update_stream_name
message_list.update_stream_name
Steve Howell