fixed a bug that it discovered


include/my_sys.h:
  move TRASH to my_sys.h from sql_list.h
sql/field.h:
  use TRASH macro
sql/item.h:
  TRASH in delete
sql/item_func.h:
  never delete item's manually!
sql/opt_range.cc:
  TRASH in delete
sql/sql_lex.h:
  TRASH in delete
sql/sql_list.h:
  move TRASH to my_sys.h from sql_list.h
sql/sql_parse.cc:
  don't use properties of deleted objects (even when it's safe)
sql/sql_select.cc:
  TRASH in delete
sql/sql_show.cc:
  TRASH in delete
sql/sql_string.h:
  TRASH in delete