Specify known good engine version

I've updated module from 2.x to 3.0 authomatically and did not updated lessphp library (kept old 0.3.8). Module version 3.0 seems incompatible with lessphp 0.3.8, so Drupal's status page showed message about not found lessphp library. It will be good to alert user to update library and add drush up compatibility (to allow Drush update library authomatically).