random temporary table name not random enough

Using the problem in bug #617517:

drizzle> create table t1 (a int primary key, b varchar(255));
Query OK, 0 rows affected (0.08 sec)

drizzle> alter table t1 engine=blackhole;
Query OK, 0 rows affected (0.14 sec)
Records: 0 Duplicates: 0 Warnings: 0

drizzle> create table t2 (a int primary key, b varchar(255));
Query OK, 0 rows affected (0.07 sec)

drizzle> alter table t2 engine=blackhole;
ERROR 1050 (42S01): Table 'temporary.#sql-a36_14' already exists