Heimdall errors, "ERROR: Failed to confirm end of file transfer sequence!"
This is a because of a bug in Heimdall v1.4 RC1 -- the version that shipped with Ubuntu 13.04. What you'll want to do is upgrade Heimdall to version 1.4 final, or the latest version..

That should do it. Run heimdall info | head -n1 to get your current version.