Fixes a bug whereby removing the next-to-last item in a profile would
lead to an obscure error, as shown at
<http://lists.gnu.org/archive/html/guix-devel/2014-12/msg00292.html>.
Reported by Ricardo Wurmus <ricardo.wurmus@mdc-berlin.de>.
* guix/profiles.scm (profile-derivation)[inputs]: Use (list info-dir
"out") instead of just INFO-DIR.