Use CHashWriter also in SignatureHash(), and for message signing

src/script.cpp

@@ -1117,10 +1117,9 @@ uint256 SignatureHash(CScript scriptCode, const CTransaction& txTo, unsigned int
     }
 
     // Serialize and hash
-    CDataStream ss(SER_GETHASH, 0);
-    ss.reserve(10000);
+    CHashWriter ss(SER_GETHASH, 0);
     ss << txTmp << nHashType;
-    return Hash(ss.begin(), ss.end());
+    return ss.GetHash();
 }