does not use trans tables

There had been two issues.
Rollback statement was recorded in binlog even though a multi-update
had not modified any non-transactional table.
The reason for this artifact was a false initial value of multi_update::transactional_tables.
Yet another artifact that explained on the bug page is that 
`ha_autocommit_or_rollback' works differently depending on whether
a transaction engine has been compiled in. 

Fixed: with setting multi_update::transactional_tables to zero at initialization
time. Multi-update on non-trans table won't cause ROLLBACK in binlog with
either compilation option.

The 2nd mentioned artifact comprises a self-standing issue (to be reported
separately).


mysql-test/r/multi_update.result:
  results changed - there is no ROLLBACK in binlog anymore as it should be
sql/sql_update.cc:
  A wrong assumption on that there were modified transactional table,
  which is nonsense at the very beginning of the query execution.