Adding a ".displaying-header-text" class to the header h1 and to the site description div inside _s_admin_header_image(). This allows the "display text with your image" toggle button to work in the admin preview under Appearance > Header.
* Use WordPress 3.4's registration method providing backward compatibility for previous versions.
* Implement shiv for get_custom_header(). props @obenland
* Allow all custom header args to be filtered via child theme/plugin.
* Update example code in DocBlock to use get_custom_header().
git-svn-id: https://wpcom-themes.svn.automattic.com/_s/@9484 d957f892-c61d-0410-b221-f235e6eecf30