Incompatibility with admin_menu module

Hi,

admin_menu is a propular replacement for Drupal's toolbar. The project page → lists currently 228,943 sites using this module.

If admin_menu is enabled, Redhen CRM can not be used. As soon as the Redhen core module is enabled, the site dies.

This error is shown in Apache's error.log:

PHP Fatal error: Call to undefined function admin_menu_tree() in /var/www/{mysite}/sites/all/modules/redhen/redhen.module on line 73

This can easily be reproduced. Disabling admin_menu allows to activate Redhen, enabling admin_menu breaks the site. And vice versa, with active admin_menu, enabling Redhen breaks the site, and disabling Redhen brings the site back.