void gtk_file_chooser_add_filter ( GtkFileChooser* chooser, GtkFileFilter* filter )
filter to the list of filters that the user can select between.
When a filter is selected, only files that are passed by that filter are displayed.
Note that the
chooser takes ownership of the filter if it is floating,
so you have to ref and sink it if you want to keep a reference.
The data is owned by the caller of the function.