You can append (or prepend, with proper changes) a directory to your include
path and preserve the original one this way:
<?php
$new_include_dir = "/home/user/php_includes";
print get_include_path() . "\n";
set_include_path(get_include_path() . ":" . $new_include_dir);
print get_include_path() . "\n";
?>
Output is:
.:/usr/local/lib/php
.:/usr/local/lib/php:/home/user/php_includes
Just remember that directories are separated by ':'
