bug#37744: Per-user profile directory hijack (CVE-2019-17365 for Nix)

[Ludovic Courtès]

I pushed the fix as 81c580c8664bfeeb767e2c47ea343004e88223c7, followed
by an updated of the ‘guix’ package in
e63b31443b29b7793e73ab04798220edc6e564fc.

Thanks everyone!

Ludo’.