Clean up mining CReserveKey to prevent crash at shutdown

Fixes issue#2687

src/bitcoinrpc.cpp

@@ -30,6 +30,10 @@ using namespace boost;
 using namespace boost::asio;
 using namespace json_spirit;
 
+// Key used by getwork/getblocktemplate miners.
+// Allocated in StartRPCThreads, free'd in StopRPCThreads
+CReserveKey* pMiningKey = NULL;
+
 static std::string strRPCUserColonPass;
 
 // These are created by StartRPCThreads, destroyed in StopRPCThreads
@@ -722,6 +726,9 @@ static void RPCAcceptHandler(boost::shared_ptr< basic_socket_acceptor<Protocol,
 
 void StartRPCThreads()
 {
+    // getwork/getblocktemplate mining rewards paid here:
+    pMiningKey = new CReserveKey(pwalletMain);
+
     strRPCUserColonPass = mapArgs["-rpcuser"] + ":" + mapArgs["-rpcpassword"];
     if ((mapArgs["-rpcpassword"] == "") ||
         (mapArgs["-rpcuser"] == mapArgs["-rpcpassword"]))
@@ -841,6 +848,8 @@ void StartRPCThreads()
 
 void StopRPCThreads()
 {
+    delete pMiningKey; pMiningKey = NULL;
+
     if (rpc_io_service == NULL) return;
 
     rpc_io_service->stop();