* jartool.c
Updated copyright year.
(progname): new variable.
(end_of_entries): new variable.
(main): open and read file when updating.
(find_entry): new function.
(looks_like_dir): new function.
(read_entries): new function.
(make_manifest): added parameter `updating'.
Call `add_file_to_jar' with `updating'.
(add_to_jar_with_dir): added parameter `updating'.
Call `add_to_jar' with `updating'.
(add_to_jar): added parameter `updating'.
Call `add_file_to_jar' with `updating'.
Don't add directories if they already exist.
(add_file_to_jar): added parameter `updating'.
Update entries if they already exist.