Fix for BUG#5949 "error code 1223 in binlog when using innobackup":

when one connection had done FLUSH TABLES WITH READ LOCK, some updates, and then COMMIT,
it was accepted but my_error() was called and so, while client got no error, error was logged in binlog.
We now don't call my_error() in this case; we assume the connection know what it does.
This problem was specific to 4.0.21. The change is needed to make replication work with existing versions of innobackup.

mysql-test/r/rpl_commit_after_flush.result

+slave stop;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+reset master;
+reset slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+slave start;
+create table t1 (a int) type=innodb;
+begin;
+insert into t1 values(1);
+flush tables with read lock;
+commit;
+unlock tables;
+drop table t1;

mysql-test/t/rpl_commit_after_flush.test

+source include/master-slave.inc;
+source include/have_innodb.inc;
+create table t1 (a int) type=innodb;
+begin;
+insert into t1 values(1);
+flush tables with read lock;
+commit;
+save_master_pos;
+connection slave;
+sync_with_master;
+# cleanup
+connection master;
+unlock tables;
+drop table t1;
+save_master_pos;
+connection slave;
+sync_with_master;

sql/lock.cc

@@ -751,9 +751,15 @@ bool wait_if_global_read_lock(THD *thd, bool abort_on_refresh, bool is_not_commi
   {
     if (thd->global_read_lock)		// This thread had the read locks
     {
+      if (is_not_commit)
         my_error(ER_CANT_UPDATE_WITH_READLOCK,MYF(0));
       (void) pthread_mutex_unlock(&LOCK_open);
-      DBUG_RETURN(1);
+      /*
+        We allow FLUSHer to COMMIT; we assume FLUSHer knows what it does.
+        This allowance is needed to not break existing versions of innobackup
+        which do a BEGIN; INSERT; FLUSH TABLES WITH READ LOCK; COMMIT.
+      */
+      DBUG_RETURN(is_not_commit);
     }
     old_message=thd->enter_cond(&COND_refresh, &LOCK_open,
 				"Waiting for release of readlock");