Improve verification checking

These problems were noticed by me and @snconnolly when testing the verification.

Removing the message as proposed in this PR, when I submit a wrong value of amount...

![screen shot 2014-03-28 at 2 40 55 pm](https://cloud.githubusercontent.com/assets/667753/2553017/62f5e5b2-b6a0-11e3-8e15-da20d3b2748c.png)

becomes...

![screen shot 2014-03-28 at 2 41 37 pm](https://cloud.githubusercontent.com/assets/667753/2553021/67b93fa4-b6a0-11e3-8964-c5053ccf4aba.png)

The reason is in the commit message: 24a2bc8.