backport fix mysqltest.cc

[Andrew Hutchings]

Request from Brian:

        revno: 1810.3723.2
        committer: <email address hidden>
        timestamp: Fri 2008-05-02 11:22:10 +0200
        message:
          Bug#36465 mysqltest should always use the --tmpdir
        diff:
        === modified file 'client/mysqltest.c'
        --- client/mysqltest.c 2008-03-23 17:53:36 +0000
        +++ client/mysqltest.c 2008-05-02 09:22:10 +0000
        @@ -1536,7 +1536,7 @@
           DBUG_ENTER("dyn_string_cmp");
           DBUG_PRINT("enter", ("fname: %s", fname));

        - if ((fd= create_temp_file(temp_file_path, NULL,
        + if ((fd= create_temp_file(temp_file_path, TMPDIR,
                                     "tmp", O_CREAT | O_SHARE | O_RDWR,
                                     MYF(MY_WME))) < 0)
             die("Failed to create temporary file for ds");