Fix unconfirmed balance, accurately report fees

[AwfulCrawler]

Problem:

Wallet may report incorrect balance before all transactions are confirmed. This is because dust amounts from change are added to fee by default, but not subtracted from the change amount when counting the wallet balance. The reported fee in the confirmation message of simplewallet also does not take this into account.

For example, try sending 1.123456 from one wallet to another.

Suggested fix:

In wallet2::transfer, after transaction details and dust amount from change has been determined,
record dust, fee and change amount according to the dust policy:

-ptx.fee += dust if dust is added to fee
-ptx.dust = dust only if dust is not added to fee and not kept in change according to dust policy;
otherwise ptx.dust = 0.
-change_dts.amount -= dust if dust is added to fee or sent elsewhere according to dust policy
-modify wallet confirmation message to accurately report fees and account for different dust policies

I removed the if statement around the confirm message in simplewallet since I prefer alway-confirm behaviour, but that is just my preference.

[iamsmooth]

Is this original work on adapted from another coin?

[AwfulCrawler]

Being as strict as possible, I copied this:

for (size_t n = 0; n < ptx_vector.size(); ++n)
{
total_fee += ptx_vector[n].fee;
...
}

from Monero. I didn't take anything else from another coin.

EDIT: I think Monero might have a similar issue from just looking at the corresponding code.

[iamsmooth]

OK thanks for the clarification. I will review it ASAP.

Thanks for our code contribution!

[AwfulCrawler]

Do you think it would be a good idea to just get rid of the dust_policy (apart from maybe the dust_threshold part)? This would also fix the bug instead of merging this pull request.