There is no reason that Intvar_log_event's constructor calls Log_event::Log_event()

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.

sql/log_event.h

@@ -529,7 +529,7 @@ class Intvar_log_event: public Log_event
 
 #ifndef MYSQL_CLIENT  
   Intvar_log_event(THD* thd_arg,uchar type_arg, ulonglong val_arg)
-    :Log_event(),val(val_arg),type(type_arg)
+    :Log_event(thd_arg,0,0),val(val_arg),type(type_arg)
   {}
   void pack_info(String* packet);
   int exec_event(struct st_relay_log_info* rli);