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### Issue description
The datadir field on the debug window displays incorrectly if the profile folder name is accented.

### How to reproduce
1. Create a profile with accented profile folder name (àèìòùáéíóú)
2. Run bitcoin core with the default datadir
3. Go to the debug window and look at the datadir field

### Expected behaviour
The datadir folder path should display correctly.

### Actual behaviour
Accented characters display as a unknown character question mark.

### Screenshots
![Debug Window](https://cloud.githubusercontent.com/assets/11365204/20029647/41dee90e-a352-11e6-8784-e5a48798d62e.png)


### Confirmed affected versions
The bug has been tested on the following implementations:

- v0.13.1 from source cross-compiled for Windows x64 on a Ubuntu 14.04 enviroment
- 0.13.0 official Windows x64 binary

### Additional debug info
Copying and pasting the text into a program that is known to support accented characters (Such as Notepad++) still displays unknown character symbols.
{
    reply->deleteLater();
    
    if (!verifySize(reply->size())) {
        Q_EMIT message(tr("Payment request rejected"),
            tr("Payment request %1 is too large (%2 bytes, allowed %3 bytes).")
                .arg(reply->request().url().toString())
                .arg(reply->size())
                .arg(BIP70_MAX_PAYMENTREQUEST_SIZE),
            CClientUIInterface::MSG_ERROR);
        return;
    }
    if (reply->error() != QNetworkReply::NoError) {
        QString msg = tr("Error communicating with %1: %2")
            .arg(reply->request().url().toString())
            .arg(reply->errorString());
        qWarning() << "PaymentServer::netRequestFinished: " << msg;
        Q_EMIT message(tr("Payment request error"), msg, CClientUIInterface::MSG_ERROR);
        return;
    }
    QByteArray data = reply->readAll();
    QString requestType = reply->request().attribute(QNetworkRequest::User).toString();
    if (requestType == BIP70_MESSAGE_PAYMENTREQUEST)
    {