Add DotProductDouble macro and use it in Mod_Q1BSP_LoadFaces

[hemebond]

Adds a new DotProductDouble macro and uses it throughout Mod_Q1BSP_LoadFaces instead of DotProduct so that lightmaps are aligned correctly. Fixes #232.

[Cloudwalk9]

This doesn't feel correct. DotProduct is a macro that makes no assumption of the datatype. You'd want to cast to double in the original DotProduct invocation. So we shouldn't need a double variant. But this smells like an internal double to float downcasting bug and casting feels like a hack without further investigation into why the lightmaps suck.

[hemebond]

Very good point. I'm still testing, but it looks like I can change mtexinfo_s->vecs from float to double and achieve the same results.