Lua integration

This contains a parallel Tupfile and Lua-Tupfile parser, and Lua versions of several test cases.  The Lua Tupfiles use .lua as an extension.  The helper built-in functions are also included.  All Lua functions are in the "tup" table.  As per Anatol's suggestion I tried squashing all the commits.  It compiles, but I'm not sure I did it correctly and I'd be glad to redo it if requested.