trac #16772: trivial bug when building OA(4,12)
Trac #15915: add discrete Gaussian samplers to Sage

This ticket adds samplers for discrete Gaussian distributions to Sage.

URL: http://trac.sagemath.org/15915
Reported by: malb
Ticket author(s): Martin Albrecht
Reviewer(s): Julian Rueth
Trac #16772: trivial bug when building OA(4,12)

There is a missing `[:k]` in the code, and Sage returns a `OA(6,12)`
even when only `OA(4,12)` is requested. Well, it TRIES to return it, as
nothing is returned by this function without being checked first `:-P`

Before
{{{
sage: OA = designs.orthogonal_array(4,12)
...
AssertionError:
}}}

After
{{{
sage: OA = designs.orthogonal_array(4,12)
sage:
}}}

URL: http://trac.sagemath.org/16772
Reported by: ncohen
Ticket author(s): Nathann Cohen
Reviewer(s): Dima Pasechnik