list: add argchecks.

* specs/list_spec.yaml (append, compare, concat, cons, depair)
(elems, enpair, filter, flatten, foldl, foldr, index_key)
(index_value, map, map_with, project, relems, rep, reverse)
(shape, sub, tail, traspose, zip_with): Specify behaviours for
missing or wrong type arguments.
8 specs/object_spec.yaml: Decouple from list implementation
details.
* lib/std/list.lua (append, compare, concat, cons, depair)
(elems, enpair, filter, flatten, foldl, foldr, index_key)
(index_value, map, map_with, project, relems, rep, reverse)
(shape, sub, tail, traspose, zip_with): Check argument types
when not disabled by _DEBUG.
* build-aux/sanity-cfg.mk: Disable bogus failures when rejecting
uppercase error messages with lib/std/list.lua.

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