Fix compilation with libtorrent v0.14

src/qtlibtorrent/qbtsession.cpp

@@ -389,8 +389,10 @@ void QBtSession::configureSession() {
   sessionSettings.cache_size = pref.diskCacheSize()*64;
   qDebug() << "Using a disk cache size of" << pref.diskCacheSize() << "MiB";
   // Disable OS cache to avoid memory problems (uTorrent behavior)
+#if LIBTORRENT_VERSION_MINOR > 14
   sessionSettings.disk_io_write_mode = session_settings::disable_os_cache_for_aligned_files;
   sessionSettings.disk_io_read_mode = session_settings::disable_os_cache_for_aligned_files;
+#endif
   // Queueing System
   if(pref.isQueueingSystemEnabled()) {
     sessionSettings.active_downloads = pref.getMaxActiveDownloads();