Fixed bug #12154: a query returned: Column <name> cannot be null.
  The problem was due to a bug in the function setup_table_map:
  the flag maybe_null was set up incorrectly for inner tables of
  nested outer joins.
join_nested.result, join_nested.test:
  Added a test case for bug #12154.


mysql-test/t/join_nested.test:
  Added a test case for bug #12154.
mysql-test/r/join_nested.result:
  Added a test case for bug #12154.
sql/mysql_priv.h:
  Fixed bug #12154: a query returned: Column <name> cannot be null.
  The problem was due to a bug in the function setup_table_map:
  the flag maybe_null was set up incorrectly for inner tables of
  nested outer joins.