Fix building with Qt 4.7.

QUrl::isLocalFile() is available starting with Qt 4.8. We can safely check for
a file:// url instead.

Qt 4.8 dropped support for OS X 10.4 / 10.5. Since we're still supporting those
we need to keep using Qt 4.7 on OS X. We might want to consider requiring at
least 10.6 on OS X with the next major release of Rockbox Utility.

Change-Id: I18998fe3c7a38773479bc7a1c32ca6e4966359e9

rbutil/rbutilqt/base/httpget.cpp

@@ -170,7 +170,7 @@ void HttpGet::requestFinished(QNetworkReply* reply)
         return;
     }
     else if(m_lastStatusCode == 200 ||
-            (reply->url().isLocalFile() && reply->error() == 0)) {
+            (reply->url().scheme() == "file" && reply->error() == 0)) {
         // callers might not be aware if the request is file:// so fake 200.
         m_lastStatusCode = 200;
         m_data = reply->readAll();