situation: modify a draft product, publish the draft, now the product becomes draft 1.0.
After awhile, changed some on the draft, draft 2.0. But not satisfied enough for publishing. Then, discard this draft. Every changes happen on the draft not the product.
In the database, after discard, the draft 2.0 should be able to turn back to the original, thus 2.0 being discared, return back to 1.0
