Replication testsuite: making the master-slave synchronization less likely to fail,

by adding sleep-and-retries (max 4 times) if MASTER_POS_WAIT() returns NULL
in sync_with_master and sync_slave_with_master.
The problem showed up only today, in MySQL 5.0 in rpl_server_id2.test,
but may affect 4.x as well, so fixing it here. Note that I am also fixing
5.0 too, with the same exact patch, because I don't want to leave 5.0 broken
until the next 4.0->4.1->5.0 merge.


client/mysqltest.c:
  in sync_with_master (and sync_slave_with_master), if MASTER_POS_WAIT() returns NULL,
  it may be that the slave SQL thread did not have time to start yes, so we sleep
  1 sec and retry, 4 times at most.
mysql-test/r/rpl_server_id2.result:
  result update
mysql-test/t/rpl_server_id2.test:
  master_slave.inc already drops the table

client/mysqltest.c

@@ -1081,7 +1081,7 @@ int do_sync_with_master2(const char* p)
   MYSQL_ROW row;
   MYSQL* mysql = &cur_con->mysql;
   char query_buf[FN_REFLEN+128];
-  int offset = 0;
+  int offset= 0, tries= 0;
   int rpl_parse;
 
   if (!master_pos.file[0])
@@ -1096,6 +1096,9 @@ int do_sync_with_master2(const char* p)
 
   sprintf(query_buf, "select master_pos_wait('%s', %ld)", master_pos.file,
 	  master_pos.pos + offset);
+
+wait_for_position:
+
   if (mysql_query(mysql, query_buf))
     die("line %u: failed in %s: %d: %s", start_lineno, query_buf,
 	mysql_errno(mysql), mysql_error(mysql));
@@ -1106,8 +1109,20 @@ int do_sync_with_master2(const char* p)
   if (!(row = mysql_fetch_row(res)))
     die("line %u: empty result in %s", start_lineno, query_buf);
   if (!row[0])
-    die("line %u: could not sync with master ('%s' returned NULL)", 
-        start_lineno, query_buf);
+  {
+    /*
+      It may be that the slave SQL thread has not started yet, though START
+      SLAVE has been issued ?
+    */
+    if (tries++ == 3)
+    {
+      die("line %u: could not sync with master ('%s' returned NULL)", 
+          start_lineno, query_buf);
+    }
+    sleep(1); /* So at most we will wait 3 seconds and make 4 tries */
+    mysql_free_result(res);
+    goto wait_for_position;
+  }
   mysql_free_result(res);
   last_result=0;
   if (rpl_parse)

mysql-test/r/rpl_server_id2.result

@@ -4,7 +4,6 @@ reset master;
 reset slave;
 drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
 slave start;
-drop table if exists t1;
 create table t1 (n int);
 reset master;
 stop slave;

mysql-test/t/rpl_server_id2.test

@@ -3,7 +3,6 @@
 
 source include/master-slave.inc;
 connection slave;
-drop table if exists t1;
 create table t1 (n int);
 reset master;
 # replicate ourselves