Don't be so generous with this jQuery selector. Fixes #3933
[sale_products] has incorrect post_type. Fixes #3934

In 2.1, woocommerce_get_product_ids_on_sale() used 'product1' instead of 'product' for post_type.
Merge pull request #3940 from scottbasgaard/master

Don't be so generous with this jQuery selector. Fixes #3933