Escape playlist data in templates.

props wonderboymusic.
fixes #27710.

Built from https://develop.svn.wordpress.org/trunk@28050


git-svn-id: http://core.svn.wordpress.org/trunk@27880 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Don't show featured images for image attachments. Remove abstractions for now.

fixes #27673.

Built from https://develop.svn.wordpress.org/trunk@28051


git-svn-id: http://core.svn.wordpress.org/trunk@27881 1a063a9b-81f0-0310-95a4-ce76da25c4cd
3.9 about page text, rough cut.

props markjaquith, nacin.
see #27713.

Built from https://develop.svn.wordpress.org/trunk@28052


git-svn-id: http://core.svn.wordpress.org/trunk@27882 1a063a9b-81f0-0310-95a4-ce76da25c4cd