Wallet: store key creation time. Calculate whole-wallet birthday.

This also encapsulate wallet-read state information into CWalletScanState.

src/walletdb.h

@@ -25,6 +25,37 @@ enum DBErrors
     DB_NEED_REWRITE
 };
 
+class CKeyMetadata
+{
+public:
+    static const int CURRENT_VERSION=1;
+    int nVersion;
+    int64 nCreateTime;
+
+    CKeyMetadata()
+    {
+        SetNull();
+    }
+    CKeyMetadata(int64 nCreateTime_)
+    {
+        nVersion = CKeyMetadata::CURRENT_VERSION;
+        nCreateTime = nCreateTime_;
+    }
+
+    IMPLEMENT_SERIALIZE
+    (
+        READWRITE(this->nVersion);
+        nVersion = this->nVersion;
+        READWRITE(nCreateTime);
+    )
+
+    void SetNull()
+    {
+        nVersion = CKeyMetadata::CURRENT_VERSION;
+        nCreateTime = GetTime();
+    }
+};
+
 /** Access to the wallet database (wallet.dat) */
 class CWalletDB : public CDB
 {
@@ -52,15 +83,31 @@ public:
         return Erase(std::make_pair(std::string("tx"), hash));
     }
 
-    bool WriteKey(const CPubKey& vchPubKey, const CPrivKey& vchPrivKey)
+    bool WriteKey(const CPubKey& vchPubKey, const CPrivKey& vchPrivKey,
+                  int64 nCreateTime)
     {
         nWalletDBUpdated++;
+
+        CKeyMetadata keyMeta(nCreateTime);
+        if (!Write(std::make_pair(std::string("keymeta"), vchPubKey),
+                   keyMeta, false))
+            return false;
+
         return Write(std::make_pair(std::string("key"), vchPubKey), vchPrivKey, false);
     }
 
-    bool WriteCryptedKey(const CPubKey& vchPubKey, const std::vector<unsigned char>& vchCryptedSecret, bool fEraseUnencryptedKey = true)
+    bool WriteCryptedKey(const CPubKey& vchPubKey,
+                         const std::vector<unsigned char>& vchCryptedSecret,
+                         int64 nCreateTime)
     {
+        const bool fEraseUnencryptedKey = true;
         nWalletDBUpdated++;
+
+        CKeyMetadata keyMeta(nCreateTime);
+        if (!Write(std::make_pair(std::string("keymeta"), vchPubKey),
+                   keyMeta, false))
+            return false;
+
         if (!Write(std::make_pair(std::string("ckey"), vchPubKey), vchCryptedSecret, false))
             return false;
         if (fEraseUnencryptedKey)