Blender Git Loki

Removed unnecessary window-close on subsequent renders. This not only causes
delays and lotsof redraw events for the desktop, it also made it impossible
to drag a renderwindow to a desired position.
Now it only re-opens on render size changes. Maybe enables to have the
window permanent on 2nd monitor for extended desktops?

Note; the 'pref position' preset in F10 still works, but only on window
open of course.