Support symbolic links in the file manager.
We didn't watch the symbolic link itself before, only the final link target. We are watching the symbolic link and the final link target now. Ugly hack: We need to work around QTBUG-15522. The inotify and kqueue based file system watcher engines (Linux + Mac) don't report changes to symbolic links. The workaround is to use the polling engine *only for the links themselves*. The only way to force the use of the polling engine is by using the auto test hook in QFileSystemWatcher.