Add ByPath, ByChecksum and Hide methods. Update unit tests to include
new methods.
Move datafileLocationID and datafileSize to util.go. Rename
dataFileLocationID to datafileLocationID in move to make the names consistent.
Add comments.
Add comments
Cleanup comment.
Clean up comments. The comments referred to the wrong type.
Rewrite createFile. Right now for this checkin both the old and the new
code exist.
Run go fmt.
Update for testing and cleanup of comments.