Better title handling for WordPress 4.1+ with proper back compat.

See #636.

Kind of rough and dirty at the moment; mostly want to get it out there as a possible approach for proper back compatibility. Thoughts?
Hi, 

Theme Check Plugin error: "REQUIRED: The theme needs to have <title> tags, ideally in the header.php file."

Maybe it is just not supported jet in the plugin (1.4.7) ... ?!

Question: I didn't get this fallback to work ... (https://make.wordpress.org/core/2014/10/29/title-tags-in-4-1/)
Can anyone help me?