sysinst with Lua support

I put a first (actually, second) diff on
http://www.netbsd.org/~mbalmer/diffs/sysinst_002.diff to make sysinst
scriptable with Lua.  The basic idea is that you can ship one or more
Lua scripts on the install media, and when sysinst starts, it will
execute this scripts.  The scripts can then either modify the
installation process or take over the control of the installation
process completely.

See the file README.Lua for general comments, english.lua and german.lua
for an idea how message catalogs can be defined, sysinst.lua for helpful
functions (especiall substituting @@name@@ variables in messages) and
installer.lua, customize.lua, and pkg.lua for installer examples.

Feedback very welcome.