Check for consitency with block header argument hash and calculated hash.

lib/block/blockheader.js

@@ -21,7 +21,22 @@ var BlockHeader = function BlockHeader(arg) {
   if (!(this instanceof BlockHeader)) {
     return new BlockHeader(arg);
   }
-  _.extend(this, BlockHeader._from(arg));
+  var info = BlockHeader._from(arg);
+  this.version = info.version;
+  this.prevHash = info.prevHash;
+  this.merkleRoot = info.merkleRoot;
+  this.time = info.time;
+  this.timestamp = info.time;
+  this.bits = info.bits;
+  this.nonce = info.nonce;
+
+  if (info.hash) {
+    $.checkState(
+      this.hash === info.hash,
+      'Argument object hash property does not match block hash.'
+    );
+  }
+
   return this;
 };
 
@@ -72,6 +87,7 @@ BlockHeader._fromObject = function _fromObject(data) {
     merkleRoot = BufferUtil.reverse(new Buffer(data.merkleRoot, 'hex'));
   }
   var info = {
+    hash: data.hash,
     version: data.version,
     prevHash: prevHash,
     merkleRoot: merkleRoot,

test/block/blockheader.js

@@ -63,6 +63,20 @@ describe('BlockHeader', function() {
       should.exist(bh.nonce);
     });
 
+    it('will throw an error if the argument object hash property doesn\'t match', function() {
+      (function() {
+        var bh = new BlockHeader({
+          hash: '000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f',
+          version: version,
+          prevHash: prevblockidbuf,
+          merkleRoot: merklerootbuf,
+          time: time,
+          bits: bits,
+          nonce: nonce
+        });
+      }).should.throw('Argument object hash property does not match block hash.');
+    });
+
   });
 
   describe('#fromJSON', function() {