Surround PGRES_SINGLE_TUPLE with an #ifdef for single row mode support.

Author: rpedela

src/binding.cc

@@ -659,7 +659,9 @@ class Connection : public ObjectWrap {
     ExecStatusType status = PQresultStatus(result);
     switch(status) {
     case PGRES_TUPLES_OK:
+#ifdef SINGLE_ROW_SUPPORTED
     case PGRES_SINGLE_TUPLE:
+#endif
       {
         EmitRowDescription(result);
         HandleTuplesResult(result);