Reduce usage of ./.

[Chris Warburton]

In a few places we're using './.', or './nix-support', or './..',
etc. usually spliced into strings. This is annoying, since it adds the
path to the Nix store, so any minor change to the code (e.g. a refactor)
will cause the hash to change, and hence the dependencies to change,
causing unnecessary rebuilding.