Three features;

- Live scanline updates while rendering
Using a timer system, each second now the tiles that are being processed
are checked if they could use display.
To make this work pretty, I had to use the threaded 'tile processor' for
a single thread too, but that's now proven to be stable.

Also note that these updates draw per layer, including ztransp progress
separately from solid render.

- Recode of ztransp OSA
Until now (since blender 1.0) the ztransp part was fully rendered and
added on top of the solid part with alpha-over. This adding was done before
the solid part applied sub-pixel sample filtering, causing the ztransp
layer to be always too blurry.

Now the ztransp layer uses same sub=pixel filter, resulting in the same
AA level (and filter results) as the solid part. Quite noticable with hair
renders.

- Vector buffer support & preliminary vector-blur Node
Using the "Render Layer" panel "Vector" pass button, the motion vectors
per pixel are calculated and stored. Accessible via the Compositor.

The vector-blur node is horrible btw! It just uses the length of the
vector to apply a filter like with current (z)blur. I'm committing it anyway,
I'll experiment with it further, and who knows some surprise code shows up!

source/blender/src/editnode.c

@@ -1178,7 +1178,7 @@ static void node_add_menu(SpaceNode *snode)
 	}
 	else if(snode->treetype==NTREE_COMPOSIT) {
 		/* compo menu, still hardcoded defines... solve */
-		event= pupmenu("Add Node%t|Render Result %x221|Composite %x222|Viewer%x201|Image %x220|RGB Curves%x209|AlphaOver %x210|Blur %x211|Filter %x212|Value %x203|Color %x202|Mix %x204|ColorRamp %x205|Color to BW %x206|Map Value %x213|Normal %x207");
+		event= pupmenu("Add Node%t|Render Result %x221|Composite %x222|Viewer%x201|Image %x220|RGB Curves%x209|AlphaOver %x210|Blur %x211|Vector Blur %x215|Filter %x212|Value %x203|Color %x202|Mix %x204|ColorRamp %x205|Color to BW %x206|Map Value %x213|Normal %x207");
 		if(event<1) return;
 	}
 	else return;