myprofile.info

name = Myprofile
core = 7.x
dependencies[] = xautoload

myprofile.install

<?php

/**
 * Implements hook_install_tasks().
 */
function myprofile_install_tasks(&$install_state) {
  $tasks = array();
  $tasks['myprofile_check_for_class'] = array();
  return $tasks;
}

function myprofile_check_for_class() {
  if (!class_exists('Isbn\Validation')) {
    trigger_error('Class not found even after profile module was enabled.');
  }
}

myprofile.profile

<?php

/**
 * Implements hook_xautoload().
 */
function myprofile_xautoload($api) {
  // Ensure the isbn library can be autoloaded.
  $api->namespaceRoot('Isbn', DRUPAL_ROOT . '/sites/all/libraries/isbn/src', FALSE);
}