Area lights and more...

- New lamp type added "Area". This uses the radiosity formula (Stoke) to
  calculate the amount of energy which is received from a plane. Result
  is very nice local light, which nicely spreads out.
- Area lamps have a 'gamma' option to control the light spread
- Area lamp builtin sizes: square, rect, cube & box. Only first 2 are
  implemented. Set a type, and define area size
- Button area size won't affect the amount of energy. But scaling the lamp
  in 3d window will do. This is to cover the case when you scale an entire
  scene, the light then will remain identical
  If you just want to change area lamp size, use buttons when you dont want
  to make the scene too bright or too dark
- Since area lights realistically are sensitive for distance (quadratic), the
  effect it has is quickly too much, or too less. For this the "Dist" value
  in Lamp can be used. Set it at Dist=10 to have reasonable light on distance
  10 Blender units (assumed you didnt scale lamp object).
- I tried square sized specularity, but this looked totally weird. Not
  committed
- Plan is to extend area light with 3d dimensions, boxes and cubes.
- Note that area light is one-sided, towards negative Z. I need to design
  a nice drawing method for it.

Area Shadow

- Since there are a lot of variables associated with soft shadow, they now
  only are available for Area lights. Allowing spot & normal lamp to have
  soft shadow is possible though, but will require a reorganisation of the
  Lamp buttons. Is a point of research & feedback still.
- Apart from area size, you now can individually set amount of samples in
  X and Y direction (for area lamp type 'Rect'). For box type area lamp,
  this will become 3 dimensions
- Area shadows have four options:
  "Clip circle" : only uses a circular shape of samples, gives smoother
  results
  "Dither" : use a 2x2 dither mask
  "Jitter" : applys a pseudo-random offset to samples
  "Umbra" : extra emphasis on area that's fully in shadow.

Raytrace speedup

- improved filling in faces in Octree. Large faces occupied too many nodes
- added a coherence check; rays fired sequentially that begin and end in
  same octree nodes, and that don't intersect, are quickly rejected
- rendering shadow scenes benefits from this 20-40%. My statue test monkey
  file now renders in 19 seconds (was 30).

Plus:

- adjusted specular max to 511, and made sure Blinn spec has again this
  incredible small spec size
- for UI rounded theme: the color "button" displayed RGB color too dark
- fixed countall() function, to also include Subsurf totals
- removed setting the 'near' clipping for pressing dot-key numpad
- when you press the buttons-window icon for 'Shading Context' the context
  automaticilly switches as with F5 hotkey

Please be warned that this is not a release... settings in files might not
work as it did, nor guaranteed to work when we do a release. :)

source/blender/src/previewrender.c

@@ -447,7 +447,7 @@ static void lamp_preview_pixel(ShadeInput *shi, LampRen *la, int x, int y, char
 		}
 		dist*=inpr;
 	}
-	else if(la->type==LA_LOCAL) dist*= shi->view[2];
+	else if ELEM(la->type, LA_LOCAL, LA_AREA) dist*= shi->view[2];
 	
 	col= 255.0*dist*la->r;
 	if(col<=0) rect[0]= 0; else if(col>=255) rect[0]= 255; else rect[0]= col;
@@ -1213,9 +1213,6 @@ void BIF_previewrender(SpaceButs *sbuts)
 	else if(tex) {
 		end_render_texture(tex);
 	}
-	else if(wrld) {
-		end_render_textures();
-	}
 	else if(la) {
 		if(R.totlamp) {
 			if(R.la[0]->org) MEM_freeN(R.la[0]->org);
@@ -1224,5 +1221,8 @@ void BIF_previewrender(SpaceButs *sbuts)
 		R.totlamp= 0;
 		end_render_textures();
 	}
+	else if(wrld) {
+		end_render_textures();
+	}
 }