For now, perhaps the best (most minimal) thing for us to do is for the gentoo
distribution to change (by patching) lines like this one:

  if path'4ti2 == "" then path'4ti2 = prefixDirectory | currentLayout#"programs"

to something like this one:

  if path'4ti2 == "" then path'4ti2 = "/usr/bin/"

In the future, we might like the "version" hash table to contain entries giving
the location of each program.  There would be entries for gfan, 4ti2, and
normaliz. The configure script would be responsible for setting those entries
up, and there would be new options for the builder of the distribution to use.
That is perhaps better than expecting the PATH environment variable of the user
to contain anything good.
