Accept absolute paths to build.
Adding embryo of VS2012 interop extension.

Currently support "compile current file with tundra".
Fix up path comparisons.
Compile on Linux.
Add a quicky make install rule

Also .PHONY was missing for `all`
Remove file install var

It's wrong, and unused.
Shouldn't be installing the unit-tests
Re-work tundra so we can install on unixes

Needed to get a little dirty, we now pass tundra's home and executable
directories to tundra.lua directly from the boot sequence in
LuaInterface.cpp.

Also tidy up the Makefile a bit more.