Checking for sufficient balance when applying a transaction.

[edg956]

When substracting the transaction's value (uint) to the sender's balance (uint) the result is also uint and the resulting value never less than 0. This allowed to make transactions from accounts without sufficient balance or previously non-existent.

[web3coach]

Well spotted. A very stupid error done in one of the overnight coding probably. I have fixed this back in December but in a different branch:

I will merge this, thanks for contributing!