Blender Git Loki

Bugfix #3133

- Rendering an image with Border didn't check for sizes smaller than 1
pixel yet.

Related to this code I found 2 other fixes:

- Themecolor set for drawing in Render Window was not restored correctly,
sometimes causing into wrong Panel (transparency) drawing.

- When rendering an image with Gauss, it now renders by default 1 pixel
extra, which gets stripped. This eliminates the "ugly" darker border
in images.
(Yes, let's make Mr. PixelCounter Goralczyk happy! :)