Fix Lua error backtrace in LuaCallback

Fix two bugs in error handling of LuaCallback::run:

1. It used the Lua function _TRACEBACK, which exists in Lua 5.0 but
   not in Lua 5.1.  In bos/stratagus SVN trunk r8495 on 2007-01-07,
   LuaCall was changed to use debug.trace instead.  Do the same to
   LuaCallback.

2. It passed the wrong Lua stack index to lua_pcall as the error
   handler function.  lua_gettop returns the index of the topmost
   value, not the index that the next pushed value will get.

Also, remove _TRACEBACK from the blacklist now that it is used neither
in Bos Wars nor in any version of Lua supported by Bos Wars.

include/luacallback.h

@@ -36,9 +36,16 @@ struct lua_State;
 class LuaCallback
 {
 	lua_State *luastate;
+
+	// Integer key of the callback function in the Lua registry.
 	int luaref;
+
+	// Number of arguments pushed for the function.
 	int arguments;
+
+	// The top of the Lua stack before pushPreamble().
 	int base;
+
 public:
 	LuaCallback(lua_State *lua, lua_Object luaref);
 	virtual ~LuaCallback();

include/script.h

@@ -112,6 +112,7 @@ extern const char *LuaToString(lua_State *l, int tableIndex, int stringIndex);
 extern int LuaToNumber(lua_State *l, int index);
 extern int LuaToNumber(lua_State *l, int tableIndex, int numberIndex);
 extern bool LuaToBoolean(lua_State *l, int index);
+extern int luatraceback(lua_State *L);
 
 extern void CclGarbageCollect(int fast);    /// Perform garbage collection
 extern void InitCcl(void);                  /// Initialise ccl

stratagus/luacallback.cpp

@@ -58,8 +58,8 @@ LuaCallback::LuaCallback(lua_State *l, lua_Object f) :
 void LuaCallback::pushPreamble() 
 {
 	base = lua_gettop(luastate);
-	lua_getglobal(luastate, "_TRACEBACK");
-	lua_rawgeti(luastate, LUA_REGISTRYINDEX, luaref);
+	lua_pushcfunction(Lua, luatraceback);		  // at base+1
+	lua_rawgeti(luastate, LUA_REGISTRYINDEX, luaref); // at base+2
 	arguments = 0;
 }
 
@@ -98,7 +98,7 @@ void LuaCallback::run()
 	int status;
 
 	 //FIXME call error reporting function
-	status = lua_pcall(luastate, arguments, 0, base);
+	status = lua_pcall(luastate, arguments, 0, base + 1);
 	if (status) {
 		const char *msg;
 		msg = lua_tostring(luastate, -1);

stratagus/script.cpp

@@ -142,7 +142,7 @@ static int report(int status, bool exitOnError)
 	return status;
 }
 
-static int luatraceback(lua_State *L) 
+int luatraceback(lua_State *L)
 {
 	lua_pushliteral(L, "debug");
 	lua_gettable(L, LUA_GLOBALSINDEX);
@@ -941,7 +941,6 @@ static bool IsBlacklistedGlobal(const char *key)
 		!strcmp(key, "ipairs") ||
 		!strcmp(key, "loadstring") ||
 		!strcmp(key, "dofile") ||
-		!strcmp(key, "_TRACEBACK") ||
 		!strcmp(key, "_VERSION") ||
 		!strcmp(key, "pairs") ||
 		!strcmp(key, "__pow") ||