How does one reduce the number of stored revisions?

How does one reduce the number of stored revision (e.g. 5 max) for post types that support revisions?

add to your wp-config.php file the following line:

// set max post revisions    
define('WP_POST_REVISIONS', 5);

source: http://codex.wordpress.org/Editing_wp-config.php#Post_Revisions