For PHP5 applications, the aggregate functionality available through classkit has been incorporated into and replaced by runkit. Per the classkit page of the PHP manual:
"Note: This extension has been replaced by runkit, which is not limited to class manipulation but has function manipulation, as well."
http://php.net/manual/en/ref.runkit.php
Per the runkit page:
" This package is meant as a feature added replacement for the classkit package. When compiled with the --enable-runkit=classkit option to ./configure, it will export classkit compatible function definitions and constants."