pop up a warning if we can't find libftd2xx

src/D2XX.cpp

@@ -60,7 +60,7 @@ struct D2XXWrapper {
         const char *libname = "libftd2xx.dylib";
         handle = dlopen(libname, RTLD_NOW);
         if (!handle) {
-            error = QString("couldn't load library ") + libname;
+            error = QString("Couldn't load library ") + libname + ".";
             return false;
         }
         LOAD_SYM(FP_OpenEx, open_ex, "FT_OpenEx");

src/Device.cpp

@@ -37,13 +37,10 @@ Device::listDevices(QString &err)
     QVector<DevicePtr> result;
     for (int i = 0; listFunctions && i < listFunctions->size(); ++i) {
         QVector<DevicePtr> tmp = (*listFunctions)[i](err);
-        if (err == "") {
-            for (int j = 0; j < tmp.size(); ++j)
-                result.append(tmp[j]);
-        }
-        else {
+        if (err == "")
+            result << tmp;
+        else
             err += "\n";
-        }
     }
     return result;
 }

src/DownloadRideDialog.cpp

@@ -101,6 +101,12 @@ DownloadRideDialog::scanDevices()
     listWidget->clear();
     QString err;
     devList = Device::listDevices(err);
+    if (err != "") {
+        QString msg = "Warning:\n\n" + err + "You may need to (re)install "
+            "the FTDI drivers before downloading.";
+        QMessageBox::warning(0, "Error Loading Device Drivers", msg, 
+                             QMessageBox::Ok, QMessageBox::NoButton);
+    }
     for (int i = 0; i < devList.size(); ++i)
         new QListWidgetItem(devList[i]->name(), listWidget);
     if (listWidget->count() > 0) {