specl: save path to spec file in `specl.specpath`.
specl: save path to spec file in `specl.specpath`.

* lib/specl/std.lua (std.package, std.io.catfile): Copied from
 stdlib.

Signed-off-by: Gary V. Vaughan <f9023000f29773649f3850298becb9544b5fd6a9@gnu.org>

gvvaughan/specl