testnet address generation and handling

[venzen]

It would be useful for bitc to be able to generate and handle testnet addresses.

Currently, when running on the testnet (-T) the app loads mainnet addresses from the wallet.cfg file, and when generating an address with

$ ./bitc -T -a myTestnetAddr

a mainnet address is generated and added to wallet.cfg.

[MuesliReep]

To work with testnet you need to manually configure base58.h

Change the following values to their testnet values:

   PUBKEY_ADDRESS       = 0,
   SCRIPT_ADDRESS       = 5,
   PRIVKEY_ADDRESS      = 128,

Testnet:

   PUBKEY_ADDRESS       = 111,
   SCRIPT_ADDRESS       = 196,
   PRIVKEY_ADDRESS      = 239,

Recompile and run again with -T. Bitc should now work with testnet