This breaks an indirect dependency of stream_data
on the channel module.
It's a verbatim code move, apart from the one-line
helper `has_history_for`. It's not totally clear
to me why the original code doesn't call into
`is_complete_for_stream_id` to early-exit, but
figuring that out is outside the scope of my
change.
It's possible that we will eventually just subsume
this tiny module into topic_list once we finish
breaking all dependencies, but we may want to
reuse this for something like Recent Topics
or other similar UIs.
It's also possible that we'll want to rename
stream_topic_history -> stream_topic_history_data
sometime soon, possibly after we clean up its
dependency on message_util soon.
Steve Howell