External JavaScript can now be referenced through drupal_add_js()

Attached upgrade routine.

Test function:

function example_external_js() {
  drupal_set_html_head('<script type="text/javascript" src="http://example.com/example.js" />');
  drupal_set_html_head('<script src="http://example.com/example.js" type="text/javascript" />');
  drupal_set_html_head('<SCRIPT SRC="http://example.com/example.js" TYPE="text/javascript" />');
}