bug#23132: Grafted system retains references to original store items

[Mark H Weaver]

Here's how to reproduce exactly what I'm seeing:

Checkout commit ffc13e753b37adb694de1d26f3ea51cf0796a8a2, which is the
commit on 'master' immediately before the merge with 'security-updates'.

>From that commit, build 'gnome-session'.  In my case, I'm doing this on
i686-linux, and here's what I see:

$ guix build gnome-session
/gnu/store/sivy5ycg2pgncahyikrqfk60cvfg0vam-gnome-session-3.18.1.2
$ guix gc --references 
/gnu/store/sivy5ycg2pgncahyikrqfk60cvfg0vam-gnome-session-3.18.1.2 | grep glib
/gnu/store/55pqh3wl085d4h033n41b7x0fg9djd1k-glib-2.46.1-bin
[...]
$ guix gc --references 
/gnu/store/55pqh3wl085d4h033n41b7x0fg9djd1k-glib-2.46.1-bin
[...]
/gnu/store/kkn66257xrrjhyhq332bndhjpz4d9x76-python-wrapper-3.4.3
[...]
$ guix gc --references 
/gnu/store/kkn66257xrrjhyhq332bndhjpz4d9x76-python-wrapper-3.4.3
/gnu/store/qrg3jza3p5281p255cx0lsqk8snbb6pq-python-3.4.3
$ guix gc --references /gnu/store/qrg3jza3p5281p255cx0lsqk8snbb6pq-python-3.4.3
[...]
/gnu/store/dgyc74zakg110dxj67z3mj9g1vk8l4xp-openssl-1.0.2f
[...]
$ guix build --log-file 
/gnu/store/dgyc74zakg110dxj67z3mj9g1vk8l4xp-openssl-1.0.2f
https://hydra.gnu.org/log/dgyc74zakg110dxj67z3mj9g1vk8l4xp-openssl-1.0.2f

      Mark