Merge branch 'master' into gonesolong

Conflicts:
	src/CMakeLists.txt
	src/b_think.cpp
	src/g_doom/a_doomweaps.cpp
	src/g_hexen/a_clericstaff.cpp
	src/g_hexen/a_fighterplayer.cpp
	src/namedef.h
	src/p_enemy.cpp
	src/p_local.h
	src/p_mobj.cpp
	src/p_teleport.cpp
	src/sc_man_tokens.h
	src/thingdef/thingdef_codeptr.cpp
	src/thingdef/thingdef_function.cpp
	src/thingdef/thingdef_parse.cpp
	wadsrc/static/actors/actor.txt
	wadsrc/static/actors/constants.txt
	wadsrc/static/actors/shared/inventory.txt

- Added register reuse to VMFunctionBuilder for FxPick's code emitter.
- Note to self: Need to reimplement IsPointerEqual and CheckClass, which
  were added to thingdef_function.cpp over the past year, as this file no
  longer exists in this branch.

src/thingdef/thingdef_parse.cpp

@@ -402,6 +402,16 @@ static void ParseUserVariable (FScanner &sc, PSymbolTable *symt, PClassActor *cl
 	}
 
 	FName symname = sc.String;
+
+	// We must ensure that we do not define duplicates, even when they come from a parent table.
+	if (symt->FindSymbol(symname, true) != NULL)
+	{
+		sc.ScriptMessage ("'%s' is already defined in '%s' or one of its ancestors.",
+			symname.GetChars(), cls ? cls->TypeName.GetChars() : "Global");
+		FScriptPosition::ErrorCounter++;
+		return;
+	}
+
 	if (sc.CheckToken('['))
 	{
 		FxExpression *expr = ParseExpression(sc, cls);