Enable and update product index checks

Because the database beneath the product price and stock status indexes hasn't really changed in recent versions, it seems worth breaking backwards compatibility to add back in that really very useful feature. I believe the stock status table has been around since at least version 1.3, and the product price index since 1.4.

Rather than querying the indexer, the code uses the Magento getTableName with the index table entity to determine the indexer table name.