Patch for CGAL-2.3

There were some bugs in Release 2.3 of CGAL that affect the polygon package, 2D extreme point calculation, 3D vector distance computations, Nef Polyhedra, and 2D and 3D alpha shapes. The following patch fixes these as well as a few typos and other cosmetic things: To install the patch, simply unpack this archive in the main CGAL directory (i.e., the one with subdirectories demo, include, and so on).