Remove #ifdef'd support for old i/o styles.

Change box terminology from "length" to "width".
 Use length terminology in common with other geometric types (usually perimeter).
Fix bugs in line arithmetic which resulted in bad intersection calculations.
Deprecate temporary unstored slope fields.
Check explicitly for intersections at endpoints to avoid rounding ugliness.
Add center() routines for lseg, path, polygon.
Add distance() routines for circle-polygon, polygon-polygon.
Check explicitly for points and polygons contained within polygons
 using an axis-crossing algorithm. (Old code just checked bounding boxes).
Add routine to convert circle-box.
*whew*