The 'BEGIN/COMMIT/ROLLBACK' log event could be filtered out if the
database is not selected by --database option of mysqlbinlog command.
This can result in problem if there are some statements in the
transaction are not filtered out.

To fix the problem, mysqlbinlog will output 'BEGIN/ROLLBACK/COMMIT' 
in regardless of the database filtering rules.

client/mysqlbinlog.cc:
  Skip the database check for BEGIN/COMMIT/ROLLBACK log events.
mysql-test/r/mysqlbinlog.result:
  Test result for bug#46998
mysql-test/t/mysqlbinlog.test:
  Added test to verify if the 'BEGIN', 'COMMIT' and 'ROLLBACK' are output
  in regardless of database filtering