TinyMCE: Restore old wordpress_adv_hidden editor parameter to enable force-showing the kitchen sink.

Merges [28181] to the 3.9 branch.

props azaozz.
fixes #27963.

Built from https://develop.svn.wordpress.org/branches/3.9@28226


git-svn-id: http://core.svn.wordpress.org/branches/3.9@28054 1a063a9b-81f0-0310-95a4-ce76da25c4cd