Up limits on alias model tris and vertices

[4LT]

Doubles the limit on alias model triangles, and doubles the limit on alias model vertices (to nearest power of 2).

Resolves #352

[andrei-drexler]

@sezero @j0zzz I think ideally these limits would be increased in QS and JoeQuake as well, to avoid incompatibilities between engines.

[4LT]

To be quite honest, I don't know why there's a per-model vertex and triangle limit, seems to me there should just be a global limit. Since models are pre-cached as opposed to loaded at runtime, there shouldn't be a negative performance impact from using a growable data structure

Ah, missed the part where MAXALIASTRIS and MAXALIASVERTS are only used for the size of global arrays; in which case it could be replaced with a malloc'd pointer.