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

This also encapsulate wallet-read state information into CWalletScanState.

src/wallet.h

@@ -123,6 +123,8 @@ public:
 
     std::set<COutPoint> setLockedCoins;
 
+    int64 nTimeFirstKey;
+
     // check whether we are allowed to upgrade (or already support) to the named feature
     bool CanSupportFeature(enum WalletFeature wf) { return nWalletMaxVersion >= wf; }
 
@@ -138,14 +140,14 @@ public:
     // Generate a new key
     CPubKey GenerateNewKey();
     // Adds a key to the store, and saves it to disk.
-    bool AddKeyPubKey(const CKey& key, const CPubKey &pubkey);
+    bool AddKeyPubKey(const CKey& key, const CPubKey &pubkey, int64 nCreateTime = 0);
     // Adds a key to the store, without saving it to disk (used by LoadWallet)
     bool LoadKey(const CKey& key, const CPubKey &pubkey) { return CCryptoKeyStore::AddKeyPubKey(key, pubkey); }
 
     bool LoadMinVersion(int nVersion) { nWalletVersion = nVersion; nWalletMaxVersion = std::max(nWalletMaxVersion, nVersion); return true; }
 
     // Adds an encrypted key to the store, and saves it to disk.
-    bool AddCryptedKey(const CPubKey &vchPubKey, const std::vector<unsigned char> &vchCryptedSecret);
+    bool AddCryptedKey(const CPubKey &vchPubKey, const std::vector<unsigned char> &vchCryptedSecret, int64 nCreateTime = 0);
     // Adds an encrypted key to the store, without saving it to disk (used by LoadWallet)
     bool LoadCryptedKey(const CPubKey &vchPubKey, const std::vector<unsigned char> &vchCryptedSecret);
     bool AddCScript(const CScript& redeemScript);