Problem: raco test <directory> mkdirs $HOME
Problem: raco test <directory> mkdirs $HOME

This breaks when you're running inside a Nix derivation.

Solution: Discover each *.rkt file ourselves, and run raco test on one at a time.

Also discovered that raco test on anything requiring (gui/*) expects
to talk to X, and crashes. Filter those out.

fractalide/fractalide,fractalide/fractalide,dmichiels/fractalide,dmichiels/fractalide,dmichiels/fractalide,fractalide/fractalide