Updated Roberto's pure xml parser for 5.1

["Joseph Stewart" <joseph.stewart@...>]

I needed to do some simple parsing (and didn't want to hack at expat)
and remembered Roberto's.

http://lua-users.org/wiki/LuaXml

I've pasted my hacked-to-work-in-5.1 underneath the 4.0 version.

Hope this is useful to someone!

-joe