mysql-test/r/subselect.result:
  test of simple row subselect
  fixed table droping
mysql-test/t/subselect.test:
  test of simple row subselect
  fixed table dropimg
sql/item.cc:
  Item_cache_str fixed to correctly store NULL and copy string value
sql/item.h:
  Item_cache_str fixed to correctly store NULL and copy string value
sql/item_cmpfunc.cc:
  support of simple row subselects
sql/item_subselect.cc:
  support of simple row subselects
sql/item_subselect.h:
  support of simple row subselects
sql/sql_class.cc:
  support of simple row subselects