status: allow --untracked=false and friends

It is natural to expect that the "--untracked" option and the
status.showuntrackedFiles configuration variable to take a Boolean
value ("do you want me to show untracked files?"), but the current
code takes nothing but "no" as "no, please do not show any".

Allow the usual Boolean values to be given, and treat 'true' as
"normal", and 'false' as "no".

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -1163,6 +1163,17 @@ static enum untracked_status_type parse_untracked_setting_name(const char *u)
 	 * Please update $__git_untracked_file_modes in
 	 * git-completion.bash when you add new options
 	 */
+	switch (git_parse_maybe_bool(u)) {
+	case 0:
+		u = "no";
+		break;
+	case 1:
+		u = "normal";
+		break;
+	default:
+		break;
+	}
+
 	if (!strcmp(u, "no"))
 		return SHOW_NO_UNTRACKED_FILES;
 	else if (!strcmp(u, "normal"))
@@ -1469,8 +1480,6 @@ static int git_status_config(const char *k, const char *v,
 	if (!strcmp(k, "status.showuntrackedfiles")) {
 		enum untracked_status_type u;
 
-		if (!v)
-			return config_error_nonbool(k);
 		u = parse_untracked_setting_name(v);
 		if (u == SHOW_UNTRACKED_FILES_ERROR)
 			return error(_("Invalid untracked files mode '%s'"), v);