Add -zapwallettxes cli/config option, used for wallet recovery

This diagnostic tool removes all "tx" records from the wallet db,
then forces a full rescan, to rebuild "tx" records accurately.

src/walletdb.cpp

@@ -684,6 +684,86 @@ DBErrors CWalletDB::LoadWallet(CWallet* pwallet)
     return result;
 }
 
+DBErrors CWalletDB::FindWalletTx(CWallet* pwallet, vector<uint256>& vTxHash)
+{
+    pwallet->vchDefaultKey = CPubKey();
+    CWalletScanState wss;
+    bool fNoncriticalErrors = false;
+    DBErrors result = DB_LOAD_OK;
+
+    try {
+        LOCK(pwallet->cs_wallet);
+        int nMinVersion = 0;
+        if (Read((string)"minversion", nMinVersion))
+        {
+            if (nMinVersion > CLIENT_VERSION)
+                return DB_TOO_NEW;
+            pwallet->LoadMinVersion(nMinVersion);
+        }
+
+        // Get cursor
+        Dbc* pcursor = GetCursor();
+        if (!pcursor)
+        {
+            LogPrintf("Error getting wallet database cursor\n");
+            return DB_CORRUPT;
+        }
+
+        while (true)
+        {
+            // Read next record
+            CDataStream ssKey(SER_DISK, CLIENT_VERSION);
+            CDataStream ssValue(SER_DISK, CLIENT_VERSION);
+            int ret = ReadAtCursor(pcursor, ssKey, ssValue);
+            if (ret == DB_NOTFOUND)
+                break;
+            else if (ret != 0)
+            {
+                LogPrintf("Error reading next record from wallet database\n");
+                return DB_CORRUPT;
+            }
+
+            string strType;
+            ssKey >> strType;
+            if (strType == "tx") {
+                uint256 hash;
+                ssKey >> hash;
+
+                vTxHash.push_back(hash);
+            }
+        }
+        pcursor->close();
+    }
+    catch (boost::thread_interrupted) {
+        throw;
+    }
+    catch (...) {
+        result = DB_CORRUPT;
+    }
+
+    if (fNoncriticalErrors && result == DB_LOAD_OK)
+        result = DB_NONCRITICAL_ERROR;
+
+    return result;
+}
+
+DBErrors CWalletDB::ZapWalletTx(CWallet* pwallet)
+{
+    // build list of wallet TXs
+    vector<uint256> vTxHash;
+    DBErrors err = FindWalletTx(pwallet, vTxHash);
+    if (err != DB_LOAD_OK)
+        return err;
+
+    // erase each wallet TX
+    BOOST_FOREACH (uint256& hash, vTxHash) {
+        if (!EraseTx(hash))
+            return DB_CORRUPT;
+    }
+
+    return DB_LOAD_OK;
+}
+
 void ThreadFlushWalletDB(const string& strFile)
 {
     // Make this thread recognisable as the wallet flushing thread