Allow getting the path of builtin.lua using minetest.get_modpath("__builtin")

src/scriptapi.cpp

@@ -3928,8 +3928,13 @@ static int l_get_current_modname(lua_State *L)
 // get_modpath(modname)
 static int l_get_modpath(lua_State *L)
 {
-	const char *modname = luaL_checkstring(L, 1);
+	std::string modname = luaL_checkstring(L, 1);
 	// Do it
+	if(modname == "__builtin"){
+		std::string path = get_server(L)->getBuiltinLuaPath();
+		lua_pushstring(L, path.c_str());
+		return 1;
+	}
 	const ModSpec *mod = get_server(L)->getModSpec(modname);
 	if(!mod){
 		lua_pushnil(L);

src/server.cpp

@@ -964,8 +964,7 @@ Server::Server(
 	}
 	
 	// Path to builtin.lua
-	std::string builtinpath = porting::path_share + DIR_DELIM + "builtin"
-			+ DIR_DELIM + "builtin.lua";
+	std::string builtinpath = getBuiltinLuaPath() + DIR_DELIM + "builtin.lua";
 
 	// Create world if it doesn't exist
 	if(!initializeWorld(m_path_world, m_gamespec.id))
@@ -4410,6 +4409,10 @@ const ModSpec* Server::getModSpec(const std::string &modname)
 	}
 	return NULL;
 }
+std::string Server::getBuiltinLuaPath()
+{
+	return porting::path_share + DIR_DELIM + "builtin";
+}
 
 v3f findSpawnPos(ServerMap &map)
 {

src/server.h

@@ -553,6 +553,7 @@ public:
 	IWritableCraftDefManager* getWritableCraftDefManager();
 
 	const ModSpec* getModSpec(const std::string &modname);
+	std::string getBuiltinLuaPath();
 	
 	std::string getWorldPath(){ return m_path_world; }