trac #17257: fix GCD_list
trac #17257: improve documentation
Trac 17257: more documentation improvements
trac #17253: Bug in explain_construction for Brouwer-van Rees
Trac #17257: GCD_list should return zero for an empty list

The function `GCD_list` from `sage.rings.integer` returns one instead of
zero for an empty list.

URL: http://trac.sagemath.org/17257
Reported by: slelievre
Ticket author(s): Samuel Lelièvre
Reviewer(s): Vincent Delecroix, Peter Bruin
Trac #17253: Bug in explain_construction for Brouwer-van Rees

Easy:
{{{
sage: print designs.orthogonal_arrays.explain_construction(9,834)
TypeError: brouwer_van_rees_with_one_truncated_column() got an
unexpected keyword argument 'explain_construction'
}}}

That can be solved by removing the build function
`brouwer_van_rees_with_one_truncated_column` that we do not need
anymore, and calling `wilson_construction` directly. The branch also
fixes a bug in `wilson_construction` when `OA=None`, i.e. only the non-
Brouwer case was handled.

Nathann

URL: http://trac.sagemath.org/17253
Reported by: ncohen
Ticket author(s): Nathann Cohen
Reviewer(s): Vincent Delecroix