Problem with 'global' keyword in Lua 5 alpha

[j.wattam-bell@...]

I've been trying Lua 5 alpha, and mostly it works fine, except that all my 
attempts to use 'global' (legally or illegally) give the same error:

   [string "Untitled 1"]:1: unexpected symbol near `global'

(a cursory examination of lparser.c (search for TK_GLOBAL) suggests 
it doesn't attempt to handle global statements)

Is this a bug, or am I doing something silly?

jwb