add CReserveScript to allow modular script keeping/returning

- use one CReserveScript per mining thread

src/wallet/wallet.cpp

@@ -2583,14 +2583,15 @@ void CWallet::UpdatedTransaction(const uint256 &hashTx)
     }
 }
 
-void CWallet::GetScriptForMining(CScript &script)
+void CWallet::GetScriptForMining(boost::shared_ptr<CReserveScript> &script)
 {
-    CReserveKey reservekey(this);
+    boost::shared_ptr<CReserveKey> rKey(new CReserveKey(this));
     CPubKey pubkey;
-    if (!reservekey.GetReservedKey(pubkey))
+    if (!rKey->GetReservedKey(pubkey))
         return;
-    script = CScript() << ToByteVector(pubkey) << OP_CHECKSIG;
-    reservekey.KeepKey();
+
+    script = rKey;
+    script->reserveScript = CScript() << ToByteVector(pubkey) << OP_CHECKSIG;
 }
 
 void CWallet::LockCoin(COutPoint& output)

src/wallet/wallet.h

@@ -28,6 +28,8 @@
 #include <utility>
 #include <vector>
 
+#include <boost/shared_ptr.hpp>
+
 /**
  * Settings
  */
@@ -680,7 +682,7 @@ public:
         }
     }
 
-    void GetScriptForMining(CScript &script);
+    void GetScriptForMining(boost::shared_ptr<CReserveScript> &script);
     void UpdateRequestCount(const CBlock& block)
     {
         LOCK(cs_wallet);
@@ -742,7 +744,7 @@ public:
 };
 
 /** A key allocated from the key pool. */
-class CReserveKey
+class CReserveKey : public CReserveScript
 {
 protected:
     CWallet* pwallet;
@@ -763,6 +765,7 @@ public:
     void ReturnKey();
     bool GetReservedKey(CPubKey &pubkey);
     void KeepKey();
+    void KeepScript() { KeepKey(); }
 };