WL#1972 "Evaluate HAVING before SELECT select-list"

- Changed name resolution for GROUP BY so that derived columns do not shadow table columns
  from the FROM clause. As a result GROUP BY now is handled as a true ANSI extentsion.
- Issue a warning when HAVING is resolved into ambiguous columns, and prefer the columns from
  the GROUP BY clause over SELECT columns.

sql/sql_help.cc

@@ -88,7 +88,7 @@ static bool init_fields(THD *thd, TABLE_LIST *tables,
     Item_field *field= new Item_field("mysql", find_fields->table_name,
                                       find_fields->field_name);
     if (!(find_fields->field= find_field_in_tables(thd, field, tables,
-						   0, TRUE, 1)))
+						   0, REPORT_ALL_ERRORS, 1)))
       DBUG_RETURN(1);
   }
   DBUG_RETURN(0);