Code review comment for lp:~michihenning/unity-scopes-api/scope-cache-dir

Following up on this:

> - I'm questioning the wisdom of what I suggested above. It seems that the
> registry is forced to do a lot more than it should have to

How is this going to work for apps? I expect that applications also will need a writable area in the file system somewhere. How do apps find out where they can write their files?