Add CGameTrace, CTraceFilter, Ray_t & trace ray related enums/defines (#254)

mathlib/mathlib_base.cpp

@@ -42,6 +42,7 @@ void Sys_Error (char *error, ...);
 #endif
 
 const QAngle vec3_angle(0,0,0);
+const Quaternion quat_identity(0,0,0,1);
 const Vector vec3_invalid( FLT_MAX, FLT_MAX, FLT_MAX );
 const int nanmask = 255<<23;