ENH: Improvements to sizing and surface conformation and memory use.

Detecting surface incursions as well as protrusions.

When a cell size is requested for a point outside the surfaces, the nearest
surface size is used to avoid an inappropriate return of the default size.

Truncating point to double before adding displacement vector to avoid memory use
growth (a linear growth for gcc 4.5 - bug, see CGAL mailing list 17/1/2011, but
grows regardless).