Blender Git Loki

New feature! (Well, replacement for the exisiting cumbersome "DispView")

Next to the "DispWindow" there are now two new choices:

- Display render output to Image Editor
- Display render output to Screen-sized Image Editor

Both options won't open a 2nd window anymore, which makes work quite more
smooth even, especially because 'focus' isn't lost. Further it fits in the
'single window UI' paradigm of Blender. Should have been done 10 years ago!

Lastly it might bypass issues with X11... having 2 windows with opengl
context is not always stable in Linux.

This option uses an identical trick as for the Compositor viewer, using an
Image block with a fixed name ("Render Result").

The flow, when invoking a Render, goes as follows:
- first it checks if there's an Image Editor visible displaying the "Render
Result", if so then it uses that area-window.
(Use this option for dual-monitor setups for example, a render will always
go to the same location then)
- else it checks if there's an Image Editor open in general, it then
assigns that window the "Render Result" Image.
- else: it searches for the largest Area in the screen, and turns that into
a temporal Image Editor showing render output.

After a render, an ESC will push back the former view, if the Area type has
changed.

Same rules apply for the "Full Screen" option. Here an ESC will always go
back to the regular Screen, and restore Area type if required.

While rendering, the queue for the renderwindow isn't handled yet, so you can
not zoom (nor get full redraws), as for the regular render window.

Existing conflicts:
- in FaceSelect mode, the Image editor enforces to display the face texture
after rendering again.
- when using an Image window for compositing, you'll lose the Viewer output
on a render.

Implementation note:
While rendering updates, nothing is drawn in frontbuffer anymore. That's
good news for b0rked OpenGL drivers (and faster). However, for the few
OpenGL cards that don't do a "swap copy" but a "swap exchange" you get
issues... has to be worked on. I'm afraid we have to drop frontbuffer
drawing altogether.

Other fixes:

- Hotkeys NumPad 1, 2, 4, 8 will set zoom levels (was half coded only?)
Use SHIFT to zoom out (smaller).

- Rendering Tile updates still had draw errors on edges of tiles, in OSA
only. (Caused by commit 4 days ago)