The problem has manifested itself in the cases when we have a nested outer join
for which it can be inferred that one of the inner tables is a single row table.


mysql-test/r/join_nested.result:
  Added a test case for bug #16260.
mysql-test/t/join_nested.test:
  Added a test case for bug #16260.
sql/sql_select.cc:
  Fixed bug #16260.
  The problem has manifested itself in the cases when we have a nested outer join
  for which it can be inferred that one of the inner tables is a single row table.
  A table is never considered as a const table if it is used in a nested join 
  that serves as an inner operand of an outer join.