Extrude edges of a Texture instead of surrounding it with transparent padding

Padding texture region with transparent region in some cases results
in appearance of display artifacts. This patch changes transparent padding
into borders extruded from a bitmap texture region.

I believe, that this change will automagically fix most of: "there is a gap between two sprites when camera moves" complaints. 

DISCLAIMER: This is not very thoroughly tested. I can only see that this commit fixed most (all?) of the glitches I've seen when moving/scaling two adjacent Sprites.