Recommit with post-review fixes.


mysql-test/r/log_tables.result:
  update result
mysql-test/t/log_tables.test:
  add a test
sql/log.cc:
  Fix NULL handling in log tables
storage/csv/ha_tina.cc:
   Explicitly check fo NULLs, when writing a row.
   We should not hope, that the null field was
   cleaned up.
   Though usually we do call Field::reset() or
   restore_row(), before calling Field::set_null(),
   this depency is neither documented nor enforced
   by other means.
mysql-test/t/log_tables-master.opt:
  New BitKeeper file ``mysql-test/t/log_tables-master.opt''