Reject valid receipts from other apps -bug 1024057

Originally this bug called for validating product
IDs but I don't think that would be a problem in
practice since restoring products is heavily tied
to ID.

@mstriemer r?
oh yeah, huh. I'll experiment with that. The ``settings.callbacks.onerror`` (going into ``callbacks``) makes it a little tricky but I'll fiddle with it.