* src/getargs.c (AS_FILE_NAME): New.
(getargs): Use it to convert DOSish file names.
* src/files.c (base_name): Rename as full_base_name to avoid
clashes with `base_name ()'.
(get_extension_index): Remove.
(filename_split): New.
(compute_base_names): N-th rewrite, using filename_split.