replication updates. This changeset seems to be working fine on test systems.

If no problems are discovered in the next week, this will make the replication
code ready for 4.0.2 release.


dbug/dbug.c:
  cleanup of my previous fix
sql/mysqld.cc:
  fixed a REALLY NASTY BUG - slave threads were being launched before 
  initialization of global thread keys. Thus if the slave thread was slow
  to start everything worked fine, but if it started quickly, we would get
  into trouble using the unitinialized keys
sql/net_pkg.cc:
  make net_printf() work with 0 error code taking the third argument as 
  format string in that case
sql/slave.cc:
  misc fix-ups and debugging instrumentations
sql/slave.h:
  added skip_log_purge member
sql/sql_class.cc:
  debugging instrumentation to track down random memory corruption
sql/sql_class.h:
  added debugging sentry to THD to track down memory corruption
sql/sql_repl.cc:
  fixed bugs in CHANGE MASTER

sql/sql_class.cc

@@ -104,6 +104,9 @@ THD::THD():user_time(0),fatal_error(0),last_insert_id_used(0),
   cond_count=0;
   convert_set=0;
   mysys_var=0;
+#ifndef DBUG_OFF
+  dbug_sentry=THD_SENTRY_MAGIC;
+#endif  
   net.vio=0;
   ull=0;
   system_thread=cleanup_done=0;
@@ -191,6 +194,7 @@ void THD::cleanup(void)
 
 THD::~THD()
 {
+  THD_CHECK_SENTRY(this);
   DBUG_ENTER("~THD()");
   /* Close connection */
   if (net.vio)
@@ -223,12 +227,16 @@ THD::~THD()
   mysys_var=0;					// Safety (shouldn't be needed)
 #ifdef SIGNAL_WITH_VIO_CLOSE
   pthread_mutex_destroy(&active_vio_lock);
+#endif
+#ifndef DBUG_OFF
+  dbug_sentry = THD_SENTRY_GONE;
 #endif  
   DBUG_VOID_RETURN;
 }
 
 void THD::awake(bool prepare_to_die)
 {
+  THD_CHECK_SENTRY(this);
   if (prepare_to_die)
     killed = 1;
   thr_alarm_kill(real_id);