(SCRUM) (part of WL#818)


mysql-test/r/subselect.result:
  test of new optimisation
mysql-test/t/subselect.test:
  test of new optimisation
sql/item_subselect.cc:
  new engine for simple IN with primary index
sql/item_subselect.h:
  new engine for simple IN with primary index
sql/sql_lex.h:
  fixed typo
sql/sql_select.cc:
  engine changing
  report_error can't be static, because it used in new engine
sql/sql_select.h:
  new JT_ type (just for information in EXPLAIN statement)
  report_error can't be static, because it used in new engine