Change "field" to "base_ring" in toric_plotter.
trac #16504: A mandatory 'nonnegative' argument for MixedIntegerLinearProgram.new_variable() until the standard changes
trac #16504: Tastes and colors ................
trac #16504: Broken doctest
trac #16504: additional doctest for nonnegative=False
Cosmetic changes
Typo in docstring for toric plotter.
Trac #16504: A mandatory 'nonnegative' argument for MixedIntegerLinearProgram.new_variable() until the standard changes

This should create an unbounded real variable:
{{{
sage: p = MixedIntegerLinearProgram()
sage: x = p.new_variable(nonnegative=False)
}}}

We should see `nonnegative` as a toggle, not as a type. The following
should also work as expected intuitively:
{{{
sage: x = p.new_variable(integer=True, nonnegative=False)
sage: x = p.new_variable(integer=True, nonnegative=True)
}}}

URL: http://trac.sagemath.org/16504
Reported by: jdemeyer
Ticket author(s): Nathann Cohen
Reviewer(s): Jeroen Demeyer
Trac #16174: Fix deprecated use of field in toric plotter

URL: http://trac.sagemath.org/16174
Reported by: novoselt
Ticket author(s): Andrey Novoseltsev
Reviewer(s): Jan Keitel