Ensure that test_quick_select doesn't return more rows than in the table

Other changes:
- In test_quick_select(), assume that if table->used_stats_records is 0
  then the table has 0 rows.
- Fixed prepare_simple_select() to populate table->used_stat_records
- Enusre that set_statistics_for_tables() doesn't cause used_stats_records
  to be 0 when using stat_tables.
- To get blackhole to work with replication, set stats.records to 2 so
  that test_quick_select() doesn't assume the table is empty.

mysql-test/main/selectivity_innodb.result

@@ -946,7 +946,7 @@ set optimizer_switch='index_condition_pushdown=off';
 EXPLAIN EXTENDED
 SELECT * FROM t1, t2 WHERE a > 9;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	range	a	a	5	NULL	1	0.00	Using where
+1	SIMPLE	t1	range	a	a	5	NULL	1	100.00	Using where
 1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	8	100.00	Using join buffer (flat, BNL join)
 Warnings:
 Note	1003	select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b`,`test`.`t2`.`c` AS `c` from `test`.`t1` join `test`.`t2` where `test`.`t1`.`a` > 9