Moving Lua source codes

[Marc Balmer <marc%msys.ch@localhost>]

Hi All

I am in the progress of

- Updating the Lua code in base from version 5.1 to version 5.2
- Commiting the kernel parts from our GSoC project, "Lua in the NetBSD
Kernel"

mrg@ suggestest that I move the Lua source code from src/external/ to
src/sys/external, which imo makes sense.  Comments requested.

The plan is to import Lua 5.2 sources in src/sys/external, then adjust
userland and kernel parts to uses sources from there, and once all
works, remove the Lua 5.1 sources from src/external.

The transition from 5.1 to 5.2 is more complicated that one would think,
especially from a C module programmers perspective (the C API changed in
a way that makes it necessary to adjust most modules).

- mbalmer