fullnode: add noScan option.

lib/bcoin/config.js

@@ -136,6 +136,7 @@ config.parseData = function parseData(data) {
   options.coinCache = bool(data.coincache);
   options.indexTX = bool(data.indextx);
   options.indexAddress = bool(data.indexaddress);
+  options.noScan = bool(data.noscan);
 
   // Mempool
   options.limitFree = bool(data.limitfree);

lib/bcoin/fullnode.js

@@ -297,6 +297,10 @@ Fullnode.prototype._open = function open(callback) {
       });
     },
     function(next) {
+      if (self.options.noScan) {
+        self.walletdb.tx.writeTip(self.chain.tip.hash, next);
+        return next();
+      }
       // Always rescan to make sure we didn't miss anything:
       // there is no atomicity between the chaindb and walletdb.
       self.walletdb.rescan(self.chain.db, next);