only turn on livereload on non-standard port access

fixes livereload from getting called in remote staging environment.
So example.com won't have livereload, but example.com:80 will.

abstract_templates/templates/layouts/components/debug_mode_head.html

@@ -1,3 +1,8 @@
+{% comment %}
+This component is inserted into the HEAD only if debug is true.
+{% endcomment %}
 <script>
-  document.write('<script src="http://' + (location.host || 'localhost').split(':')[0] + ':35729/livereload.js?snipver=1"></' + 'script>')
+  if (location.port) {
+    document.write('<script src="http://' + (location.host || 'localhost').split(':')[0] + ':35729/livereload.js?snipver=1"></' + 'script>')
+  }
 </script>