add game version specific differences

This implements the subtle differences found in the three variants
of DOOM.EXE version 1.9. The code was taken from PrBoom+ and
Chocolate Doom, respectively. I decided to go without the original
comments, the code has been commented well enough in other source
ports. @fragglet Do you think these are all the relevant differences?

Source/p_enemy.c

@@ -2133,6 +2133,16 @@ void A_BossDeath(mobj_t *mo)
     }
   else
     {
+      // [FG] game version specific differences
+      if (demo_compatibility && gameversion < exe_ultimate)
+      {
+        if (gamemap != 8)
+          return;
+
+        if (mo->type == MT_BRUISER && gameepisode != 1)
+          return;
+      }
+      else
       switch(gameepisode)
         {
         case 1:

Source/p_mobj.c

@@ -469,8 +469,13 @@ floater:
     {
       // hit the floor
 
-      if (mo->flags & MF_SKULLFLY)
+      // [FG] game version specific differences
+      int correct_lost_soul_bounce = !demo_compatibility || gameversion >= exe_ultimate;
+
+      if (correct_lost_soul_bounce && mo->flags & MF_SKULLFLY)
+      {
 	mo->momz = -mo->momz; // the skull slammed into something
+      }
 
       if (mo->momz < 0)
 	{
@@ -496,6 +501,12 @@ floater:
 
       mo->z = mo->floorz;
 
+      // [FG] game version specific differences
+      if (!correct_lost_soul_bounce && mo->flags & MF_SKULLFLY)
+      {
+	mo->momz = -mo->momz;
+      }
+
       if (!((mo->flags ^ MF_MISSILE) & (MF_MISSILE | MF_NOCLIP)))
 	{
 	  P_ExplodeMissile (mo);

Source/p_telept.c

@@ -72,7 +72,11 @@ int EV_Teleport(line_t *line, int side, mobj_t *thing)
           if (!P_TeleportMove(thing, m->x, m->y, false)) // killough 8/9/98
             return 0;
 
+          // [FG] game version specific differences
+          if (demo_compatibility && gameversion != exe_final)
+          {
           thing->z = thing->floorz;
+          }
 
           if (player)
             player->viewz = thing->z + player->viewheight;