VCS code duplication and subordinate

[Patrick Hetu]

I guess the VCS subordinates will have a polling_schedule variable and
will be responsible to configure the cron job.

> Good idea. Also see my branch with more SCM for node.js. How do you think it
> should be done? We need some relation to somehow tell the app charm that new
> content is available. The problem is that relations only work inside hooks,
> so my cron based polling won't be able to signal new content through the
> relation.