games/doom: add bug compatibility switches (thanks qu7uux)

these emulate bugs present in select versions of the released doom executables.
they are required to correctly play demos recorded with these but affect the
gameplay, so should be otherwise disabled.

-nobounce: lost souls don't bounce off floors and ceilings like intended due
to a misplaced check; this is fixed from ultimate doom on, but doom and doom2
are still affected.

-noztele: in final doom 1.9, things' altitude was erroneously not set to the
floor's height after teleporting. this was fixed in later versions of the
executables.

examples of desyncing demos:
(plutonia.wad, without -noztele) http://doomedsda.us/lmps/946/2/30pl2646.zip
(doom2.wad, without -nobounce) http://doomedsda.us/lmps/945/3/30nm2939.zip

sys/src/games/doom/d_main.c

@@ -90,6 +90,9 @@ boolean         drone;
 
 boolean		singletics = false; // debug flag to cancel adaptiveness
 
+/* bug compatibility with various versions of doom */
+boolean		noztele;
+boolean		nobounce;
 
 
 //extern int soundVolume;
@@ -736,6 +739,10 @@ void D_DoomMain (void)
     respawnparm = M_CheckParm ("-respawn");
     fastparm = M_CheckParm ("-fast");
     devparm = M_CheckParm ("-devparm");
+    if (M_CheckParm ("-noztele") && gamemode == commercial)
+	noztele = 1;
+    if (M_CheckParm ("-nobounce") && (gamemode == commercial || gamemode == registered))
+	nobounce = 1;
     if (M_CheckParm ("-altdeath"))
 	deathmatch = 2;
     else if (M_CheckParm ("-deathmatch"))

sys/src/games/doom/p_local.h

@@ -60,6 +60,8 @@
 // follow a player exlusively for 3 seconds
 #define	BASETHRESHOLD	 	100
 
+extern	boolean	noztele;
+extern	boolean	nobounce;
 
 
 //

sys/src/games/doom/p_mobj.c

@@ -285,10 +285,7 @@ void P_ZMovement (mobj_t* mo)
     {
 	// hit the floor
 
-	// Note (id):
-	//  somebody left this after the setting momz to 0,
-	//  kinda useless there.
-	if (mo->flags & MF_SKULLFLY)
+	if (!nobounce && mo->flags & MF_SKULLFLY)
 	{
 	    // the skull slammed into something
 	    mo->momz = -mo->momz;
@@ -310,6 +307,9 @@ void P_ZMovement (mobj_t* mo)
 	}
 	mo->z = mo->floorz;
 
+	if (nobounce && mo->flags & MF_SKULLFLY)
+	    mo->momz = -mo->momz;
+
 	if ( (mo->flags & MF_MISSILE)
 	     && !(mo->flags & MF_NOCLIP) )
 	{

sys/src/games/doom/p_telept.c

@@ -102,7 +102,8 @@ EV_Teleport
 		if (!P_TeleportMove (thing, m->x, m->y))
 		    return 0;
 
-		thing->z = thing->floorz;  //fixme: not needed?
+		if(!noztele)
+			thing->z = thing->floorz;
 		if (thing->player)
 		    thing->player->viewz = thing->z+thing->player->viewheight;