`'__return_false'` is a string that ends up evaluating as true so we're using file manifest all the time.

We actually just want to opt-in to using the file manifest approach.
Drop the time we wait until we report the backup process dead.

Waiting longer means an increased delay in getting the backup restarted again.
Merge pull request #114 from humanmade/fix-file-manifest

Misc fixes to the file manifest backup approach