CLEANUP: hlua: use hlua_pusherror() where relevant

CLEANUP: hlua: use hlua_pusherror() where relevant

In hlua_map_new(), when error occurs we use a combination of luaL_where,
lua_pushfstring and lua_concat to build the error string before calling
lua_error().

It turns out that we already have the hlua_pusherror() macro which is
exactly made for that purpose so let's use it.

It could be backported to all stable versions to ease code maintenance.