instead of Log_event::Log_event(THD*, ...) when the event is built in the master
to be written in the binlog.
Rand_log_event already used the good constructor, so there really is no reason
for Intvar_log_event to be an exception.
This fixes a test failure of last night (which appeared after I removed a useless
e.server_id=thd->server_id in log.cc; in fact this line was not useless because
it hid the bad constructor).
Replication tests pass, with Valgrind too.