filter_type is the description of the type of file, wild_card represents
the file extension of the files to be listed in the standard file-open and
file-save dialog boxes. filter_type and wild_card are standard
character strings (can be replaced by @) but %ft cannot be used to change this
information dynamically at run time (use get_filtered_file@ instead).
%ft can be used more than once to supply a number of different filters.