Store version bytes and be able to serialize them in CExtPubKey

CExtPubKey does not store the version bytes for the extended public key.
We store these so that a CExtPubKey can be serialized and deserialized with
the same version bytes.

src/pubkey.cpp

@@ -352,6 +352,18 @@ void CExtPubKey::Decode(const unsigned char code[BIP32_EXTKEY_SIZE]) {
     if ((nDepth == 0 && (nChild != 0 || ReadLE32(vchFingerprint) != 0)) || !pubkey.IsFullyValid()) pubkey = CPubKey();
 }
 
+void CExtPubKey::EncodeWithVersion(unsigned char code[BIP32_EXTKEY_WITH_VERSION_SIZE]) const
+{
+    memcpy(code, version, 4);
+    Encode(&code[4]);
+}
+
+void CExtPubKey::DecodeWithVersion(const unsigned char code[BIP32_EXTKEY_WITH_VERSION_SIZE])
+{
+    memcpy(version, code, 4);
+    Decode(&code[4]);
+}
+
 bool CExtPubKey::Derive(CExtPubKey &out, unsigned int _nChild) const {
     out.nDepth = nDepth + 1;
     CKeyID id = pubkey.GetID();

src/pubkey.h

@@ -17,6 +17,7 @@
 #include <vector>
 
 const unsigned int BIP32_EXTKEY_SIZE = 74;
+const unsigned int BIP32_EXTKEY_WITH_VERSION_SIZE = 78;
 
 /** A reference to a CKey: the Hash160 of its serialized public key */
 class CKeyID : public uint160
@@ -283,6 +284,7 @@ public:
 };
 
 struct CExtPubKey {
+    unsigned char version[4];
     unsigned char nDepth;
     unsigned char vchFingerprint[4];
     unsigned int nChild;
@@ -305,6 +307,8 @@ struct CExtPubKey {
 
     void Encode(unsigned char code[BIP32_EXTKEY_SIZE]) const;
     void Decode(const unsigned char code[BIP32_EXTKEY_SIZE]);
+    void EncodeWithVersion(unsigned char code[BIP32_EXTKEY_WITH_VERSION_SIZE]) const;
+    void DecodeWithVersion(const unsigned char code[BIP32_EXTKEY_WITH_VERSION_SIZE]);
     bool Derive(CExtPubKey& out, unsigned int nChild) const;
 };