Server crashed during a sort order optimization
of a dependent subquery:

SELECT
    (SELECT t1.a FROM t1, t2
      WHERE t1.a = t2.b AND t2.a = t3.c
      ORDER BY t1.a)
  FROM t3;


Bitmap of tables, that the reference to outer table
column uses, in addition to the regular table bit
has the OUTER_REF_TABLE_BIT bit set.
The only_eq_ref_tables function traverses this map
bit by bit simultaneously with join->map2table list.
Obviously join->map2table never contains an entry
for the OUTER_REF_TABLE_BIT pseudo-table, so the
server crashed there.


The only_eq_ref_tables function has been modified
to traverse regular table bits only like the
update_depend_map function (resetting of the
OUTER_REF_TABLE_BIT there is enough, but
resetting of the whole set of PSEUDO_TABLE_BITS
is used there for sure).


mysql-test/r/order_by.result:
  Added test case for bug #39844.
mysql-test/t/order_by.test:
  Added test case for bug #39844.
sql/sql_select.cc:
  Bug #39844: Query Crash Mysql Server 5.0.67
  
  The only_eq_ref_tables function has been modified
  to traverse regular table bits only like the
  update_depend_map function (resetting of the
  OUTER_REF_TABLE_BIT there is enough, but
  resetting of the whole set of PSEUDO_TABLE_BITS
  is used there for sure).