Blender Git Loki

This is patch #6833
https://projects.blender.org/tracker/index.php?func=detail&aid=6833&group_id=9&atid=127

It adds the option when creating a new "screen" to create an empty one
(one with one window)

While its one more click, I think this is pretty dang useful. If people
want to revert it feel free, and we can talk about it.
This seems more consistant with the Scene bar though so I figured it was safe
to add it.

Kent