PHP notice thrown in views_xhtml_views_plugins()

The Views hook_views_plugin() hook in views_xhtml.views.inc has the value for the 'module' array key of the array returned to Views as a string w/o quotes. PHP appears to look for a defined constant for views_xhtml. The patch places quotes around 'views_xhtml' which makes the PHP notice go away.

For what it's worth the error message showed up when I was on update.php and is straight from PHP assuming you have your site set to show errors on screen:

array(5) {
  ["%type"]=>
  string(6) "Notice"
  ["%message"]=>
  string(61) "Use of undefined constant views_xhtml - assumed 'views_xhtml'"
  ["%function"]=>
  string(27) "views_xhtml_views_plugins()"
  ["%file"]=>
  string(83) "/opt/www/tng-fresh/sites/all/modules/contrib/views_datasource/views_xhtml.views.inc"
  ["%line"]=>
  int(19)
}