mutually-nested subqueries

Queries of the form

  SELECT * FROM (SELECT 1) AS t1,
                (SELECT 2) AS t2,...
                (SELECT 32) AS t32

caused the "Too high level of nesting for select" error
as if the query has a form

  SELECT * FROM (SELECT 1 FROM (SELECT 2 FROM (SELECT 3 FROM...


The table_factor parser rule has been modified to adjust
the LEX::nest_level variable value after every derived table.