BUG: Ensure that all child pages are deleted (regardless of ShowInMenu status) under enforce_strict_hierarchy.

Also updated SiteTree YML test data to match.

code/model/SiteTree.php

@@ -1562,7 +1562,7 @@ class SiteTree extends DataObject implements PermissionProvider,i18nEntityProvid
 		parent::onBeforeDelete();
 		
 		// If deleting this page, delete all its children.
-		if(SiteTree::config()->enforce_strict_hierarchy && $children = $this->Children()) {
+		if(SiteTree::config()->enforce_strict_hierarchy && $children = $this->AllChildren()) {
 			foreach($children as $child) {
 				$child->delete();
 			}

tests/model/SiteTreeTest.yml

@@ -56,6 +56,7 @@ Page:
     Title: Staff
     URLSegment: my-staff
     Parent: =>Page.about
+    ShowInMenus: 0
   products:
     Title: Products
     CanEditType: OnlyTheseUsers