This is needed for Sphinx 7.1+

…ns_fix_in_contour_plot

This also fixes a bug in region_plot, so that plot_points are not
passed in calls to other functions via options.

This is because a @options decorator's argument are automatically popped
from "options" dict as soon as the function it decorates has an arg
with the same name.

In the change we reduce the number of positional arguments of
region_plot; thus the corresponding args of @options have to be popped
manually in the function body; we don't pop plot_points, to
pass it correctly in function calls.