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.