fix some warnings

Great job, I will use your function of signature verify.
After review your code, I fix some warnings, I think it's wlll make it better.

By the way, You can use jQuery selector in a more efficient way.

ex: var $hash = $('hash'); $hash.focus(); $hash.val(Crypto.util.bytesToHex(bytes));

I haven't changed your brainwallet.js, because it's your own business logic. :)

Thank you for your job.