completion: add more parameter value completion

This adds value completion for a couple more paramters. To make it
easier to maintain these hard coded lists, add a comment at the original
list/code to remind people to update git-completion.bash too.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

apply.c

@@ -56,6 +56,10 @@ static int parse_whitespace_option(struct apply_state *state, const char *option
 		state->ws_error_action = correct_ws_error;
 		return 0;
 	}
+	/*
+	 * Please update $__git_whitespacelist in git-completion.bash
+	 * when you add new options.
+	 */
 	return error(_("unrecognized whitespace option '%s'"), option);
 }