Perform winding order check on unrotated polygons.

We remove the rotation step that occurred prior to clipping, so that
clipping processes unrotated polygons.  Note that clip regions are
defined relative to the rotated globe, so clipping now needs a rotation
parameter.

Rather than moving the rotation step so it occurs after clipping, the
rotation occurs as part of clipping, using the rotation parameter to
rotate streamed points.  Alternatively, points could be clipped against
a rotated clip region, and then subsequently rotated as a separate step,
but this seems slightly less efficient.

Fixes #1453.