The file ProofNegotiation.java was moved from the obsolete
directory how-tos/proof-negotiation and was renamed to
NegotiateProof.java to be consistent with the scripts in
other languages in the directory negotiate-proof.
But this Java script was not tested or validated, and all the java
directory must be completed (by a Java developer) (with steps and other)
like for other "how-tos" scripts.