Reintegrate LUA script engine

[Bean]

Hi,

The LUA script engine is now back to the main trunk, I also fix a
small bug which cause it to fail in 64-bit platform.

--
Bean

Project: https://launchpad.net/burg
Document: https://help.ubuntu.com/community/Burg
Mailing list: http://groups.google.com/group/burg-devel

[Bean]

Hi,

loadfile needs to use c function such as fopen, which doesn't exist in
grub, so I disable it previously. I have written a proper wrapper for
the fs calls so that loadfile works all right now. For example:

grub.cfg:
. /test1.lua

test1.lua
#!lua

func = loadfile("/test2.lua")
print("AAA")
print("BBB")
pcall(func)

test2.lua
#!lua
print("CCC")

Result:
AAA
BBB
CCC