Closes #1293 by adding z_getoperationresult and making z_getoperationstatus idempotent.

src/rpcclient.cpp

@@ -101,6 +101,7 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "z_sendmany", 1},
     { "z_sendmany", 2},
     { "z_getoperationstatus", 0},
+    { "z_getoperationresult", 0},
     { "z_importkey", 1 }
 };