Okay, I got it. In includes/post.php:
SEARCH
if($_POST["name"]) {
$name = $_POST["name"];
setcookie("name",$_POST["name"],COOKIE_EXPIRES);
} else {
array_push($errors,$ERRORS["namerequired"]);
}
REPLACE
$name = $_POST["name"] ? name($_POST["name"]) : "Anonymous";
setcookie("name",$_POST["name"],COOKIE_EXPIRES);
Also the changes in js/ochiba.js as described by hr above.
I have taken this code from the tripcode and it works but it would be even more elegant if there was a check, whether a cookie_name exists before posting, and if there is none:
setcookie("name","Anonymous",COOKIE_EXPIRES);
So that when one has never posted on the board before, the name is filled in with "Anonymous" by default.
EDIT: Next step might be to use a variable instead of "Anonymous" which by default is empty and throws the name-required-error. Once set in conf.php it uses whatever the Admin specified and throws no error anymore. Well, just thinking here. :)