Split client_context::after_command() into two stages, before

sending result to client and after the result was sent. Added
s_result state to client_context states.

src/dbms_simulator.cpp

@@ -392,7 +392,8 @@ private:
             }
             after_statement();
         }
-        after_command();
+        after_command_before_result();
+        after_command_after_result();
         return err;
     }