During installation of an app we rewrite and clean up the
deployed export directory, but don't actually export it.
Instead we export only the "current" version of the application
when we run update_exports (passing in which app changed). This way
we ensure that any newly exported files in the current app are exported
before we remove all dangling symlinks.
To make the symlinks properly dangle we also make the export symlinks
point use the "current" and "active" symlinks so non-current deployed
dirs don't keep an old symlink from being removed.
When installed a branch is made current, and we list this in list-apps.
This means nothing atm, but will be used to limit exports to the current
branch of an app.
Alexander Larsson