Add stack traces on Lua warnings

This means that any deprecation message triggered from Lua now explains exactly where it triggered.

The message still triggers only once, so you would need multiple passes to fix every case, but it seems like an improvement.

src/scripting/lua_kernel_base.cpp

@@ -135,8 +135,13 @@ static void impl_warn(void* p, const char* msg, int tocont) {
 	warning.seekp(0, std::ios::end);
 	warning << msg << ' ';
 	if(!tocont) {
-		auto& lk = lua_kernel_base::get_lua_kernel<lua_kernel_base>(reinterpret_cast<lua_State*>(p));
-		lk.add_log_to_console(warning.str());
+		auto L = reinterpret_cast<lua_State*>(p);
+		luaW_getglobal(L, "debug", "traceback");
+		lua_push(L, warning.str());
+		lua_pushinteger(L, 2);
+		lua_call(L, 2, 1);
+		auto& lk = lua_kernel_base::get_lua_kernel<lua_kernel_base>(L);
+		lk.add_log_to_console(luaL_checkstring(L, -1));
 		warning.str(prefix);
 	}
 }