Lua 5 stack traceback / unwind

["Michael Cumming" <Mike.C@...>]

In lua 4, we would get a stack trace back if there was an error using
lua_dobuffer.

In lua 5, we are using luaL_loadbuffer followed by lua_pcall.  If there
is an error, there is no stack trace back.

How do we implement this in lua 5?

Mike