* Cross comp. & callCabalProjectToNix/callStackToNix
This fixes an issue where the these IFD functions fail because they try
to build and run a cross compiled nix-tools on the build system.
It may also help if there are cross compilation issues with
setup-depends (they also access the buildPackages).
* Align stack-to-nix ifd with plan-to-nix ifd
This also fixes the restricted/pure eval issues with callStackToNix.
I've also made the tests run in restricted mode to catch these kinds of
issues.
