Script:

<?php
function t ($s, $val, $test=false) {
    echo $s." : ".ini_get($s)."\n";
    $old = ini_set($s,$val);
    if ($old == false && $test)
        echo "\tcould not change ini setting\n";
    echo $s." : ".ini_get($s)."\n";
    ini_alter($s, $old);
    echo $s." : ".ini_get($s)."\n";
}

// following line dumps core
t("session.cookie_domain","php.net");
// next line will dump core too
// t("session.cookie_path","/application");
?>

Config:

./configure  --with-gd=/usr/local/gd1.3 \
--with-config-file-path=/usr/local/php4 \
--enable-track-vars \
--enable-magic-quotes --enable-bcmath \
--with-mysql --with-xml \
--enable-wddx \
--enable-sockets --enable-sysvsem \
--enable-sysvshm --enable-yp \
--enable-inline-optimization \
--enable-calendar --enable-ftp \
--enable-trans-sid \
--with-pgsql=/usr/local/pgsql/

I am using the Zend optimizer:
[php.ini]
magic_quotes_gpc=0
max_execution_time=300
error_log=/usr/local/apache/logs/php_error_log
zend_optimizer.optimization_level=15
zend_extension="/usr/local/Zend/lib/ZendOptimizer.so