Refresh TFTP code from upstream

The TFTP code that JNode uses to implement the TFTP client/server comes from an external source (Apache commons I think). The version of the code we are currently using is a bit buggy. (For example, it fails if the file that you are trying to GET does not already exist locally.)

Assuming that there are no larger implications, we should upgrade to a newer (hopefully non-buggy) version of the TFTP (etc) code from the upstream source.