If this variable is set at 1, the color of the upper left pixel of true
color textures (24 bit TGA images) is used as overlay transparency color, instead
of black. This way the background of sprites or skins can be set to any color,
thus avoiding black seams by antialiasing to a black
background. The variable only affects entities or bitmaps loaded afterwards,
and thus should be set before loading a level.
1 - the color of the upper left pixel is the overlay color.
0 - black (0,0,0) is the overlay color (default).
d3d_autotransparency = 1; // upper left pixel color is transparent for all afterwards loaded textures