Consistently apply 'preview_post_link' filter. fixes #19378.

git-svn-id: https://core.svn.wordpress.org/trunk@23560 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Twelve: fix double featured images in Front Page Template, closes #22943.

git-svn-id: https://core.svn.wordpress.org/trunk@23561 1a063a9b-81f0-0310-95a4-ce76da25c4cd