Tell portscout to ignore x11-fonts/psftools

The upstream HTTP server is configured to redirect to
psftools-1.0.10.tar.gz with a 301 when the requested filename is
similar enough to it. This leads to portscout finding bogus tarballs
like psftools-{1.0.11,1.0.12,...,1.1.10}.tar.gz which are really
psftools-1.0.10.tar.gz.