make receivePubkey compatible with dark wallet

I had been using this formula for the receiveKeypair:

scanKeypair + payloadKeypair + sharedKeypair

However, Dark Wallet uses this formula:

payloadKeypair + sharedKeypair

It is not actually necessary to add the scanKeypair in order to have all the
features of stealth addresses, at least as far as I can tell. So in order to
bring my implementation closer to Dark Wallet's, I have removed the scanKeypair
from this calculation.

lib/expmt/stealthaddress.js

@@ -65,7 +65,7 @@ StealthAddress.prototype.getSharedKeypair = function(senderKeypair) {
 
 StealthAddress.prototype.getReceivePubkey = function(senderKeypair) {
   var sharedKeypair = this.getSharedKeypair(senderKeypair);
-  var pubkey = Pubkey(this.scanPubkey.point.add(sharedKeypair.pubkey.point).add(this.payloadPubkey.point));
+  var pubkey = Pubkey(this.payloadPubkey.point.add(sharedKeypair.pubkey.point));
 
   return pubkey;
 };

lib/expmt/stealthkey.js

@@ -46,14 +46,14 @@ Stealthkey.prototype.getSharedKeypair = function(senderPubkey) {
 
 Stealthkey.prototype.getReceivePubkey = function(senderPubkey) {
   var sharedKeypair = this.getSharedKeypair(senderPubkey);
-  var pubkey = Pubkey({point: this.scanKeypair.pubkey.point.add(sharedKeypair.pubkey.point).add(this.payloadKeypair.pubkey.point)});
+  var pubkey = Pubkey({point: this.payloadKeypair.pubkey.point.add(sharedKeypair.pubkey.point)});
 
   return pubkey;
 };
 
 Stealthkey.prototype.getReceiveKeypair = function(senderPubkey) {
   var sharedKeypair = this.getSharedKeypair(senderPubkey);
-  var privkey = Privkey({bn: this.scanKeypair.privkey.bn.add(sharedKeypair.privkey.bn).add(this.payloadKeypair.privkey.bn).mod(Point.getN())});
+  var privkey = Privkey({bn: this.payloadKeypair.privkey.bn.add(sharedKeypair.privkey.bn).mod(Point.getN())});
   var key = Keypair({privkey: privkey});
   key.privkey2pubkey();
 

test/stealthkey.js

@@ -103,12 +103,12 @@ describe('Stealthkey', function() {
   describe('#isForMe', function() {
 
     it('should return true if it (the transaction or message) is for me', function() {
-      var pubkeyhash = new Buffer('0db7f06cffb913322e211e8b0688efe8ff52aa8d', 'hex');
+      var pubkeyhash = new Buffer('3cb64fa6ee9b3e8754e3e2bd033bf61048604a99', 'hex');
       stealthkey.isForMe(senderKeypair.pubkey, pubkeyhash).should.equal(true);
     });
 
     it('should return false if it (the transaction or message) is not for me', function() {
-      var pubkeyhash = new Buffer('ffb7f06cffb913322e211e8b0688efe8ff52aa8d', 'hex');
+      var pubkeyhash = new Buffer('00b64fa6ee9b3e8754e3e2bd033bf61048604a99', 'hex');
       stealthkey.isForMe(senderKeypair.pubkey, pubkeyhash).should.equal(false);
     });
 

test/stealthmessage.js

@@ -12,7 +12,7 @@ describe('StealthMessage', function() {
   var payloadKeypair = KDF.buf2keypair(new Buffer('key1'));
   var scanKeypair = KDF.buf2keypair(new Buffer('key2'));
   var fromKeypair = KDF.buf2keypair(new Buffer('key3'));
-  var enchex = '3867dce7be22e8551512b25f329b51fd5fe8ecfe0381c7831a20c7c9ec88dcf092ea3683261798ccda991ed65a3a54a036d8125dec0381c7831a20c7c9ec88dcf092ea3683261798ccda991ed65a3a54a036d8125dec9f86d081884c7d659a2feaa0c55ad015aca97de5af3a34a0f47eee0a1f7774dcb759187555003282bd23b047bceb5b2f2c1ee35b8f0be1fda7a41424f6cc8030559c8c32ea8cc812860f4c8123f1417a';
+  var enchex = 'f557994f16d0d628fa4fdb4ab3d7e0bc5f2754f20381c7831a20c7c9ec88dcf092ea3683261798ccda991ed65a3a54a036d8125dec0381c7831a20c7c9ec88dcf092ea3683261798ccda991ed65a3a54a036d8125dec9f86d081884c7d659a2feaa0c55ad01560ba2904d3bc8395b6c4a6f87648edb33db6a22170e5e26f340c7ba943169210234cd6a753ad13919b0ab7d678b47b5e7d63e452382de2c2590fb57ef048f7b3';
   var encbuf = new Buffer(enchex, 'hex');
   var ivbuf = Hash.sha256(new Buffer('test')).slice(0, 128 / 8);
   var sk = Stealthkey().set({payloadKeypair: payloadKeypair, scanKeypair: scanKeypair});