Bug 1009877 - Display Auto-run JS option only if script tag is present;

r=pomax@mozillafoundation.org
Gah, just realised we'll have to test for `/<\/script\s*>/i` instead, as the way it tests now it might also fire for `<script-definition>` or other custom elements that start with "script". Since closing tags may not contain any attributes, testing for the closing tag should allow us to test the full tag name.