(struct dir_attr, flag_path, remove_trailing_slashes,

(struct dir_attr, flag_path, remove_trailing_slashes,
re_protect, make_path_private, target_directory_operand, do_copy,
cp_option_init, decode_preserve_arg, main): Use bool when appropriate.
(target_directory_operand): Do not clear *NEW_DST if stat
succeeds.  It's not necessary in that case, as *NEW_DST is always
false already.
(do_copy): Rewrite slightly to avoid need for "unreachable" comment.
(main): Use EXIT_SUCCESS, EXIT_FAILURE instead of 0, 1.