LevelDB block and coin databases

Split off CBlockTreeDB and CCoinsViewDB into txdb-*.{cpp,h} files,
implemented by either LevelDB or BDB.

Based on code from earlier commits by Mike Hearn in his leveldb
branch.

src/txdb-leveldb.h

@@ -0,0 +1,46 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2012 The Bitcoin developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+#ifndef BITCOIN_TXDB_LEVELDB_H
+#define BITCOIN_TXDB_LEVELDB_H
+
+#include "main.h"
+#include "leveldb.h"
+
+/** CCoinsView backed by the LevelDB coin database (coins/) */
+class CCoinsViewDB : public CCoinsView
+{
+protected:
+    CLevelDB db;
+public:
+    CCoinsViewDB();
+
+    bool GetCoins(uint256 txid, CCoins &coins);
+    bool SetCoins(uint256 txid, const CCoins &coins);
+    bool HaveCoins(uint256 txid);
+    CBlockIndex *GetBestBlock();
+    bool SetBestBlock(CBlockIndex *pindex);
+    bool BatchWrite(const std::map<uint256, CCoins> &mapCoins, CBlockIndex *pindex);
+};
+
+/** Access to the block database (blktree/) */
+class CBlockTreeDB : public CLevelDB
+{
+public:
+    CBlockTreeDB(const char* pszMode="r+") : CLevelDB(GetDataDir() / "blktree") { }
+private:
+    CBlockTreeDB(const CBlockTreeDB&);
+    void operator=(const CBlockTreeDB&);
+public:
+    bool WriteBlockIndex(const CDiskBlockIndex& blockindex);
+    bool ReadBestInvalidWork(CBigNum& bnBestInvalidWork);
+    bool WriteBestInvalidWork(const CBigNum& bnBestInvalidWork);
+    bool ReadBlockFileInfo(int nFile, CBlockFileInfo &fileinfo);
+    bool WriteBlockFileInfo(int nFile, const CBlockFileInfo &fileinfo);
+    bool ReadLastBlockFile(int &nFile);
+    bool WriteLastBlockFile(int nFile);
+    bool LoadBlockIndexGuts();
+};
+
+#endif // BITCOIN_TXDB_LEVELDB_H