Postfix for bug#48321

Some test cases set ANSI_QUOTES in sql_mode.
So we have to use single quotes to quote literal strings.

mysql-test/include/diff_tables.inc

@@ -68,7 +68,7 @@ while ($_diff_i) {
 # and connect the appropriate server.
   let $_pos= `SELECT LOCATE(':', '$_diff_table')`;
   let $_diff_conn=`SELECT SUBSTR('$_diff_table', 1, $_pos-1)`;
-  if (`SELECT "XX$_diff_conn" <> "XX"`) {
+  if (`SELECT 'XX$_diff_conn' <> 'XX'`) {
     let $_diff_table=`SELECT SUBSTR('$_diff_table', $_pos+1)`;
     connection $_diff_conn;
   }