ls-files: mark exclude options as NONEG

Running "git ls-files --no-exclude" will currently segfault, as its
option callback does not handle the "unset" parameter.

In theory this could be used to clear the exclude list, but it is not
clear how that would interact with the other exclude options, nor is the
current code capable of clearing the list. Let's just disable the broken
option.

Note that --no-exclude-from will similarly segfault, but
--no-exclude-standard will not. It just silently does the wrong thing
(pretending as if --exclude-standard was specified).
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/ls-files.c

@@ -548,15 +548,16 @@ int cmd_ls_files(int argc, const char **argv, const char *cmd_prefix)
 			    N_("show resolve-undo information")),
 		{ OPTION_CALLBACK, 'x', "exclude", &exclude_list, N_("pattern"),
 			N_("skip files matching pattern"),
-			0, option_parse_exclude },
+			PARSE_OPT_NONEG, option_parse_exclude },
 		{ OPTION_CALLBACK, 'X', "exclude-from", &dir, N_("file"),
 			N_("exclude patterns are read from <file>"),
-			0, option_parse_exclude_from },
+			PARSE_OPT_NONEG, option_parse_exclude_from },
 		OPT_STRING(0, "exclude-per-directory", &dir.exclude_per_dir, N_("file"),
 			N_("read additional per-directory exclude patterns in <file>")),
 		{ OPTION_CALLBACK, 0, "exclude-standard", &dir, NULL,
 			N_("add the standard git exclusions"),
-			PARSE_OPT_NOARG, option_parse_exclude_standard },
+			PARSE_OPT_NOARG | PARSE_OPT_NONEG,
+			option_parse_exclude_standard },
 		OPT_SET_INT_F(0, "full-name", &prefix_len,
 			      N_("make the output relative to the project top directory"),
 			      0, PARSE_OPT_NONEG),