MINOR when a parent page is unpublished, unpublish all related virtua…

…l pages, includes test coverage (from r94777) (from r96771)

git-svn-id: svn://svn.silverstripe.com/silverstripe/open/modules/sapphire/trunk@102399 467b73ca-7a2a-4603-9d3b-597d59a354a9

core/model/SiteTree.php

@@ -1997,6 +1997,15 @@ function doUnpublish() {
 
 		$this->write();
 
+		// Unpublish all virtual pages that point here
+		// This coupling to the subsites module is frustrating, but difficult to avoid.
+		if(class_exists('Subsite')) {
+			$virtualPages = Subsite::get_from_all_subsites('VirtualPage', "CopyContentFromID = {$this->ID}");
+		} else {
+			$virtualPages = DataObject::get('VirtualPage', "CopyContentFromID = {$this->ID}");
+		}
+		if ($virtualPages) foreach($virtualPages as $vp) $vp->doUnpublish();
+
 		$this->extend('onAfterUnpublish');
 	}