TinyMCE: when parsing [caption] and the width attribute is missing, recreate it from the image tag width, fixes #23103
Built from https://develop.svn.wordpress.org/trunk@27426


git-svn-id: http://core.svn.wordpress.org/trunk@27273 1a063a9b-81f0-0310-95a4-ce76da25c4cd
TinyMCE: remove border-radius and padding from placeholder images, props avryl, see #27106
Built from https://develop.svn.wordpress.org/trunk@27427


git-svn-id: http://core.svn.wordpress.org/trunk@27274 1a063a9b-81f0-0310-95a4-ce76da25c4cd
TinyMCE: add the <hr> plugin and button, see #27159
Built from https://develop.svn.wordpress.org/trunk@27428


git-svn-id: http://core.svn.wordpress.org/trunk@27275 1a063a9b-81f0-0310-95a4-ce76da25c4cd