Description:
------------
If a callback function for array_map calls array_map again for array arguments, it is possible to cause infinite recursion for arrays with cyclic references.

While this is NOT a bug and everything works as expected, it would be nice to have a flag to array_map, that address this issue.

Current syntax for array_map prevents adding new parameters at the end (arguments for the callback go there). However an additional optional parameter may be added at the begining. Since the first argument is always a callback, the form with additional flags can be easily distinguished:
array_map(callback, array, ...)                <-- old form
array_map(non-callback, callback, array, ...)  <-- with flags as 1st arg

Test script:
---------------
// WARNING: CAUSES INFINITE RECURSION!

function fn($arg) {
    if (is_array($arg)) {
        return array_map('fn', $arg);
    } else {
        return $arg; // in a real code something will be done here
    }
}

$array = array(1, 2, 3);
$array[] = &$array;

fn($array);