Bug#12713 "Error in a stored function called from a SELECT doesn't

cause ROLLBACK of statement", part 1. Review fixes.

Do not send OK/EOF packets to the client until we reached the end of 
the current statement.
This is a consolidation, to keep the functionality that is shared by all 
SQL statements in one place in the server.
Currently this functionality includes:
- close_thread_tables()
- log_slow_statement().

After this patch and the subsequent patch for Bug#12713, it shall also include:
- ha_autocommit_or_rollback()
- net_end_statement()
- query_cache_end_of_result().

In future it may also include:
- mysql_reset_thd_for_next_command().

sql/sql_select.cc

@@ -898,7 +898,6 @@ JOIN::optimize()
       }
       if (res > 1)
       {
-        thd->fatal_error();
         error= res;
         DBUG_PRINT("error",("Error from opt_sum_query"));
 	DBUG_RETURN(1);
@@ -14454,6 +14453,7 @@ calc_group_buffer(JOIN *join,ORDER *group)
       default:
         /* This case should never be choosen */
         DBUG_ASSERT(0);
+        my_error(ER_OUT_OF_RESOURCES, MYF(0));
         join->thd->fatal_error();
       }
     }