Throw new IO exception when failing to closing a CacheOutputStream (ie move to cache dir and so on)
Followup from review. Removed the getFreeSpace method and documented some
the _new files are handled correctly now.
Moved the _new postfix to a new_ prefix, as this was easier to filter and deal with, especially if we will work with extensions later on (gz up front)
The DeferringArchives now do NOT include new_ files when listing content. Ie. the new_ file will remain untill someone requests them for some reason.