Peercoin: Fix no listen mode
          Without network discovery addresses broadcasted by peers
          are not recorded by IP address manager, causing connection
          issues for no listen mode (-listen=0).

Symptom:
    Connection issues under no listen mode (listen=0)

Diagnosis:
    vfReachable is not initialized if network discovery (Discover())
    is skipped.
    Message handler (ProcessMessage()) would then not pass the addresses
    received from peers (message 'addr') to IP address manager (addrman),
    resulting in insufficient connections under no listen mode.
    vfReachable is introduced in commit 090e5b40. So it appears to be a
    bitcoin regression introduced since bitcoin v0.7.
Cancel the best block when a duplicate stake is received
Added functional tests
Merge pull request #75 from sigmike/cancel_duplicate_stake

Cancel the best block when a duplicate stake is received
Merge pull request #76 from sigmike/peercoin_functional_tests

Added functional tests
Fixed miner tests
Fixed checkpoint tests
Added OP_COINSTAKE opcode

Push 1 if the transaction is a CoinStake.
Else push 0.
Added cold minting script

Accepts only signature from the minting key when inside a CoinStake.
Accepts only signature from the spending key when inside all other transactions.
Added RPC addcoldmintingaddress
Improved tests
Minting with a minting-only key