What (basically) does views/includes/plugins.inc line 9 views_include('base') actually do?
From views.module:

/**
 * Include views .inc files as necessary.
 */
function views_include($file) {
  static $used = array();
  if (!isset($used[$file])) {
    require_once './' . drupal_get_path('module', 'views') . "/includes/$file.inc";
  }

  $used[$file] = TRUE;
}


so to your question, it is trying to load up base.inc out of the Views module includes directory.  Unfortunately, for whatever reason, the views module itself doesn't appear to be loading up (and thus defining the function to begin with).