Stop using parameters as code comments

[foodprocessor]

Some functions in file cache take file lock items as parameters, just to signal to the coder that the lock should be acquired before calling the function. This change removes that and replaces it with code comments.

This also improves and simplifies file rename logic. The biggest change in the logic is that we no longer reverse a rename when the local rename fails. Instead, we just delete the local source file and point any open handles to the new name. This allows us to complete renames in more cases, without any risk of data loss.