move wallet code to separate file

This introduces two new source files, keystore.cpp and wallet.cpp with
corresponding headers. Code is moved from main and db, in a preparation
for a follow-up commit which introduces the classes CWallet and CKeyStore.

src/keystore.cpp

@@ -0,0 +1,33 @@
+// Copyright (c) 2009-2011 Satoshi Nakamoto & Bitcoin developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file license.txt or http://www.opensource.org/licenses/mit-license.php.
+
+#include "headers.h"
+#include "db.h"
+
+
+
+//////////////////////////////////////////////////////////////////////////////
+//
+// mapKeys
+//
+
+std::vector<unsigned char> GenerateNewKey()
+{
+    RandAddSeedPerfmon();
+    CKey key;
+    key.MakeNewKey();
+    if (!AddKey(key))
+        throw std::runtime_error("GenerateNewKey() : AddKey failed");
+    return key.GetPubKey();
+}
+
+bool AddKey(const CKey& key)
+{
+    CRITICAL_BLOCK(cs_mapKeys)
+    {
+        mapKeys[key.GetPubKey()] = key.GetPrivKey();
+        mapPubKeys[Hash160(key.GetPubKey())] = key.GetPubKey();
+    }
+    return CWalletDB().WriteKey(key.GetPubKey(), key.GetPrivKey());
+}