add per-map overrides to disable graphics features

The mapper has now the choice to disable several graphics features on
the client (for his map only, of course). The overrides are stored in
the map header.

mapoverride_nowaterreflect

  If "1", water reflection is disabled. Useful, when odd water colours
  are used to emulate other liquids that are not supposed to be that
  reflective.

mapoverride_limitwaveheight

  If "1", waveheight is capped at 0.1 max. Useful for small water
  areas (like puddles), where higher waves would look weird.

mapoverride_nostencilshadows

  If "1", stencil shadows are disabled. On clients, where stencil shadows
  are otherwise enabled, blob shadows are used instead. If shadows are
  disabled anyway, they stay disabled. Useful for dim maps, where hard
  shadows make no sense.


The player is free to ignore any of those overrides:

ignoreoverride_nowaterreflect

  If "1", mapoverride_nowaterreflect is ignored and regular client
  settings are used.

ignoreoverride_limitwaveheight

  If "1", mapoverride_limitwaveheight is ignored, and "waveheight" is
  used unchanged.

ignoreoverride_nostencilshadows

  If "1", mapoverride_nostencilshadows is ignored.


DOCREF mapoverride_nowaterreflect ignoreoverride_nowaterreflect
DOCREF mapoverride_limitwaveheight ignoreoverride_limitwaveheight
DOCREF mapoverride_nostencilshadows ignoreoverride_nostencilshadows

source/src/rendermodel.cpp

@@ -671,7 +671,7 @@ void endmodelbatches(bool flush)
             }
             renderbatchedmodel(b.m, bm);
         }
-        if(dynshadow && b.m->hasshadows() && (!reflecting || refracting) && (!stencilshadow || !hasstencil || stencilbits < 8))
+        if(dynshadow && b.m->hasshadows() && (!reflecting || refracting) && (!effective_stencilshadow || !hasstencil || stencilbits < 8))
         {
             loopvj(b.batched)
             {
@@ -780,7 +780,7 @@ void rendermodel(const char *mdl, int anim, int tex, float rad, const vec &o, fl
     if(!OUTBORD(x, y))
     {
         sqr *s = S(x, y);
-        if(!(anim&ANIM_TRANSLUCENT) && dynshadow && m->hasshadows() && (!reflecting || refracting) && (!stencilshadow || !hasstencil || stencilbits < 8))
+        if(!(anim&ANIM_TRANSLUCENT) && dynshadow && m->hasshadows() && (!reflecting || refracting) && (!effective_stencilshadow || !hasstencil || stencilbits < 8))
         {
             vec center(o.x, o.y, s->floor);
             if(s->type==FHF) center.z -= s->vdelta/4.0f;