[m-rev.] for review: document failrue conditions for list.split/4

[Julien Fischer]

On Thu, 2 Jun 2016, Julien Fischer wrote:

> Document failure conditions for list.split/4.
>
> Improve test coverage of list.split_list, list.drop and list.take.
>
> library/list.m:
>    Document the failure conditions for split_list/4.
>
>    Document that det_split_list/4 will also throw an exception for N < 0.
>
> tests/hard_coded/split_list.{m,exp}:
>    Test for list.split_list/4.
>
> tests/hard_coded/take_and_drop.m:
>    Ditto for list.take/3 and list.drop/3.
>
> tests/hard_coded/Mmakefile:
>    Add the new tests.

I won't commit this one as-is, but instead modify take and split
as per the discussion in this thread and modify the tests
so that that they check the relationship between split_list,
take and drop.

Julien.