PackageMaker project accordingly; added CGAL-absolute.pmproj which a
PackageMaker project for the CGAL package with hardcoded absolute paths
(CGAL.pmproj contains only relative paths); absolute paths are necessary for
the command-line version of PackageMaker to work with the project file.
Updated README.txt file with instructions on how to build the MacOSX
distribution using the create_macosx_installer script (can be found at the
developer_scripts directory).