Add a helper function for remote locations

Add a helper function that says whether a location should be
considered remote. To determine this, we look at the filesystem
type reported by gvfs, and say 'remote' for sftp, webdav, ftp,
nfs and cifs.

gtk/gtkfilesystem.h

@@ -118,6 +118,8 @@ gboolean	_gtk_file_info_consider_as_directory (GFileInfo *info);
 /* GFile helper functions */
 gboolean	_gtk_file_has_native_path (GFile *file);
 
+gboolean        _gtk_file_consider_as_remote (GFile *file);
+
 G_END_DECLS
 
 #endif /* __GTK_FILE_SYSTEM_H__ */