Prevent multiple hierarchical posts with the same slug from being displayed in single post template.

fixes #28611.
Built from https://develop.svn.wordpress.org/trunk@28803


git-svn-id: http://core.svn.wordpress.org/trunk@28612 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Don't kill an empty search query.

see #11330.
Built from https://develop.svn.wordpress.org/trunk@28804


git-svn-id: http://core.svn.wordpress.org/trunk@28613 1a063a9b-81f0-0310-95a4-ce76da25c4cd