With a pruned wallet possible in master I believe we should expose the option in the GUI.

The Main tab in preferences will offer a chance to toggle the node type and size.
<img width="612" alt="pruning_gui_off" src="https://cloud.githubusercontent.com/assets/216917/8766147/834fb842-2e2c-11e5-94b0-c342132243bf.png">
<img width="612" alt="pruning_gui_on" src="https://cloud.githubusercontent.com/assets/216917/8766148/8351a0c6-2e2c-11e5-841b-af02fd77ff44.png">

The prune size UI should not permit sizes less than 550.

{
    ui->statusLabel->clear();
    if (model && model->isRestartRequired()) {
        showRestartWarning(true);
    }
}
void OptionsDialog::updateProxyValidationState()
{
    QValidatedLineEdit *pUiProxyIp = ui->proxyIp;
    QValidatedLineEdit *otherProxyWidget = (pUiProxyIp == ui->proxyIpTor) ? ui->proxyIp : ui->proxyIpTor;
    if (pUiProxyIp->isValid() && (!ui->proxyPort->isEnabled() || ui->proxyPort->text().toInt() > 0) && (!ui->proxyPortTor->isEnabled() || ui->proxyPortTor->text().toInt() > 0))
    {
        setOkButtonState(otherProxyWidget->isValid()); 
        clearStatusLabel();
    }
    else
    {
        setOkButtonState(false);
        ui->statusLabel->setStyleSheet("QLabel { color: red; }");
        ui->statusLabel->setText(tr("The supplied proxy address is invalid."));
    }
}
void OptionsDialog::updateDefaultProxyNets()