filename includes a
directory path, then the requestor will open with that path as its
current working directory.
WARNING: gtk_file_selection_set_filename is deprecated and should not be used in newly-written code.
gtkFileSelectionSetFilename(object, filename)objectfilenamefilename must have a trailing
directory separator.
The encoding of filename is preferred GLib file name encoding, which
may not be UTF-8. See gFilenameFromUtf8().