Refactor model-loading code.

Instead of loading an MD2 straight into memory (and operating on it
that way), instead use a different memory structure.

This new approach has us doing the byte scale+translate beforehand
(so we have vec3_ts when it comes time to draw). Models take up a
bit more memory now. (You'll get over it.)

Visually, this should be identical to stock Q2 alias model rendering.
Identify connected submodels of each model.
Add vertex rotation/translation fixup code.

Add code to readjust normals as well.
Compute shading on-the-fly instead of using table lookup.

Move r_avertexnormals definition: we only use this when loading models now.

Fix lack of null termination in loaded model skin names.
Merge branch 'master' of github.com:bstreiff/quake2