LIMIT fixed
AVG & STD with subselect fixed
join_free fixed to be depended queries compatible
sort_default removed from SELECT_LEX


mysql-test/r/subselect.result:
  new subselect tests
mysql-test/t/subselect.test:
  new subselect tests
sql/item.cc:
  marking as depended _ALL_ subselects under select from wich depend
sql/item_subselect.cc:
  limit fixed
  TODO added
sql/sql_class.cc:
  AVG & STD function with subselects fixed
sql/sql_lex.h:
  sort_default removed
sql/sql_parse.cc:
  limit fixed
sql/sql_select.cc:
  fixed to be subselect compatible
sql/sql_yacc.yy:
  sort_default removed