Add a debug message that gets printed if TakeDevice fails

This can be useful while debugging why the TakeDevice request fails.

src/session_consolekit.cpp

@@ -175,6 +175,8 @@ int ConsoleKitSession::openRestricted(const QString &fileName)
 
     const QDBusMessage reply = QDBusConnection::systemBus().call(message);
     if (reply.type() == QDBusMessage::ErrorMessage) {
+        qCDebug(KWIN_CORE, "Failed to open %s device (%s)",
+                qPrintable(fileName), qPrintable(reply.errorMessage()));
         return -1;
     }
 

src/session_logind.cpp

@@ -181,6 +181,8 @@ int LogindSession::openRestricted(const QString &fileName)
 
     const QDBusMessage reply = QDBusConnection::systemBus().call(message);
     if (reply.type() == QDBusMessage::ErrorMessage) {
+        qCDebug(KWIN_CORE, "Failed to open %s device (%s)",
+                qPrintable(fileName), qPrintable(reply.errorMessage()));
         return -1;
     }