add chain._checkReward.

lib/bcoin/chain.js

@@ -691,6 +691,21 @@ Chain.prototype._checkInputs = function _checkInputs(block, prev, flags, callbac
   });
 };
 
+Chain.prototype._checkReward = function _checkReward(block) {
+  var claimed, actual;
+
+  claimed = block.txs[0].getOutputValue();
+  actual = bcoin.block.reward(block.height);
+
+  for (i = 1; i < block.txs.length; i++)
+    actual.iadd(block.txs[i].getFee());
+
+  if (claimed.cmp(actual) > 0)
+    return false;
+
+  return true;
+};
+
 Chain.prototype._fillBlock = function _fillBlock(block, callback) {
   var self = this;