Don't try to add orphaned pages' parents' slugs to the page URL

[filosofo]

If a page becomes orphaned---in other words, if a page points to a parent object that doesn't exist any more---get_page_uri() doesn't sanity check that the parent object actually exists.

Patch does the check without any extra work, by moving stuff around.

checks the status of the parent page before adding it to uri

This seems to fix the problem in version (3.5-alpha-21751).

Code used to test:
<?php
$uri = get_page_uri(get_the_ID());
echo '<a href="'. $uri .'">The Page</a>';
?>
The output :
<a href="sample-page/thistoo">The Page</a>

My main concern is I was not using permalinks...

Original patch, refreshed

Same as 15963.2.diff, with proper formatting