Follow-up for the fix for bug #46947 "Embedded SELECT without

FOR UPDATE is causing a lock".
 
This patch tries to address problems which were exposed 
during backporting of original patch to 5.1 tree.
 
- It ensures that we don't change locking behavior of simple
  SELECT statements on InnoDB tables when they are executed
  under LOCK TABLES ... READ and with @@innodb_table_locks=0.
  Also we no longer pass TL_READ_DEFAULT/TL_WRITE_DEFAULT 
  lock types, which are supposed to be parser-only, to 
  handler::start_stmt() method.
- It makes check_/no_concurrent_insert.inc auxiliary scripts 
  more robust against changes in test cases that use them
  and also ensures that they don't unnecessarily change 
  environment of caller.

mysql-test/include/check_no_concurrent_insert.inc

@@ -20,6 +20,9 @@
 --disable_result_log
 --disable_query_log
 
+# Reset DEBUG_SYNC facility for safety.
+set debug_sync= "RESET";
+
 if (`SELECT '$restore_table' <> ''`)
 {
 --eval create table t_backup select * from $restore_table;
@@ -71,5 +74,8 @@ if (`SELECT '$restore_table' <> ''`)
 drop table t_backup;
 }
 
+# Clean-up. Reset DEBUG_SYNC facility after use.
+set debug_sync= "RESET";
+
 --enable_result_log
 --enable_query_log