Change PPCoin mention in signed messages
Change PPCoin mention in signed messages

This change makes signed message incompatible with previous versions of
Peercoin.

ppcoin/ppcoin,glv2/peerunity,glv2/peerunity,peercoin/peercoin,peercoin/peercoin,ppcoin/ppcoin,peercoin/peercoin,ppcoin/ppcoin,peercoin/peercoin,glv2/peerunity,peercoin/peercoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,ppcoin/ppcoin,DigitalPandacoin/pandacoin,peercoin/peercoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,glv2/peerunity