When in review, if we edit a card in such a way that when we go back
to the review activity the displayed card should change (e.g. changing
the deck of the card), we need to make sure that the new card's answer
is not shown.
This is what my change makes sure of.
Merge pull request #171 from pabloem/iss1504-card-answer-revealed-early

Iss1504 card answer revealed early