Implement roll-back limit for reorganisation

Closes #713.

src/main.h

@@ -56,6 +56,8 @@ static const unsigned int DEFAULT_BLOCK_PRIORITY_SIZE = DEFAULT_BLOCK_MAX_SIZE /
 static const bool DEFAULT_ALERTS = true;
 /** Minimum alert priority for enabling safe mode. */
 static const int ALERT_PRIORITY_SAFE_MODE = 4000;
+/** Maximum reorg length we will accept before we shut down and alert the user. */
+static const unsigned int MAX_REORG_LENGTH = COINBASE_MATURITY - 1;
 /** Maximum number of signature check operations in an IsStandard() P2SH script */
 static const unsigned int MAX_P2SH_SIGOPS = 15;
 /** The maximum number of sigops we're willing to relay/mine in a single tx */