Thu Oct 31 20:33:54 EDT 2019

temporary nix-build cache hack

Here's how to do it:

- in the builder script, put a hard-coded "cd" to the directory that
  has the cache.

- when done, remove the "cd" command

This is a minimal change that forces you to actually remove the
impurity to perform a pristine build, and when that build succeeds you
can commit to source control.