Changed default BLOCK version to 3.
Changed default BLOCK version to 3.

POW blocks MUST always be version 2 or less to be accepted in netcoin
1.2 wallets.  POS blocks must be version 3 or higher to enable serialize
logic to handle their extra fields. POS blocks are a hard fork from 1.2
wallets.

birty/net2,birty/net2,Meee32/net2,birty/net2,birty/net2,Meee32/net2,Meee32/net2,Meee32/net2,Meee32/net2,birty/net2