Generate culled and non-culled variants of translucent textures.

A known way to workaround broken deluxe maps on translucent textures is to cull the translucent texture.

For example culling the trak5 glass workarounds this bug:

• Deluxe maps are wrong on and near transparent surfaces close to a skybox. Unvanquished/Unvanquished#2908

Sloth disabled culling on translucent textures, and it makes sense when the texture is within the world, like when used on a glass door, or that you can walk both outside and inside a building having windows made of glass.

But when the glass surface is sealing the world and the other side of the glass is the void, we can cull those textures, and it happens that culling such textures helps q3map2 to not do garbage with deluxe mapping (maybe q3map2 is trying to blend the deluxemaps of both side into one).

So this code generates an extra _cull variant, here an example with trak5 glass:

textures/shared_trak5/glass
{
	qer_editorImage textures/shared_trak5_src/glass_d
	qer_trans 0.50

	cull                none
	surfaceparm         trans

	{
		diffuseMap textures/shared_trak5_src/glass_d
		blend blend
	}
}

textures/shared_trak5/glass_cull
{
	qer_editorImage textures/shared_trak5_src/glass_d
	qer_trans 0.50

	surfaceparm         trans

	{
		diffuseMap textures/shared_trak5_src/glass_d
		blend blend
	}
}