Improve handling of commit_unknown_results

[andrewchambers]

There are a few places where retry of commit_unknown_results errors causes problems:

We unlinked a file, we retry on commit_unknown_results then the file is not found causing a spurious error. It seems to me in this situation one sensible solution is an io error and not a file not found error. To solve this fully we might need to associate a token with the unlink operation so we can make unlink idempotent.

We created a file and retry on commit_unknown_results, this will cause a spurious file already exists error - this case is easily solved by checking if the file that exists has the inode we are trying to create - inodes are unique in hafs.

We renamed a file and retry oncommit_unknown_results, this will cause a spurious file not found error.