Move the entity transform setup into the clients.

This has several benifits:
  o The silly issue with alias model pitches being backwards is kept out
    of the renderer (it's a quakec thing: entites do their pitch
    backwards, but originally, only alias models were rotated. Hipnotic
    did brush entity rotations in the correct direction).
  o Angle to frame vector conversions are done only when the entity's
    angles vector changes, rather than every frame. This avoids a lot of
    unnecessary trig function calls.
  o Once transformed, an entity's frame vectors are always available.
    However, the vectors are left handed rather than right handed (ie,
    forward/left/up instead of forward/right/up): just a matter of
    watching the sign. This avoids even more trig calls (flag models in
    qw).
  o This paves the way for merging brush entity surface rendering with the
    world model surface rendering (the actual goal of this patch).
  o This also paves the way for using quaternions to represent entity
    orientation, as that would be a protocol change.

nq/include/client.h

@@ -380,6 +380,8 @@ void CL_ClearTEnts (void);
 void CL_Init_Entity (struct entity_s *ent);
 void CL_ParseTEnt (void);
 void CL_SignonReply (void);
+void CL_TransformEntity (struct entity_s *ent, const vec3_t
+						 angles, qboolean force);
 void CL_RelinkEntities (void);
 void CL_ClearEnts (void);