Added a test case for bug #5896.
sql_select.cc:
  Fixed the problem of ignoring on expressions depending
  only on outer table when outer table either contains
  1 row or is guaranteed to return only 1 row (bug #5896).


sql/sql_select.cc:
  Fixed the problem of ignoring on expressions depending
  only on outer tables when outer tables either contained
  1 row or is guaranteed to return not more than 1 row.
  (bug #5896).
mysql-test/t/join_outer.test:
  Added a test case for bug #5896.
mysql-test/r/join_outer.result:
  Added a test case for bug #5896.