Sage comes with optional packages.  Unfortunately they have to be downloaded
and installed after the port is built, and preferably before the port is
installed (see note 4).  But because of the security risk of downloading files
without checksums, they can only be installed manually as follows:

cd /usr/ports/math/sage
make build
work/sage-*/sage -optional			# See note 1.
work/sage-*/sage -i $OPTIONAL_PACKAGE_NAME	# See note 2.
make install					# See note 3.

1.  This command gives a list of the optional packages available.
2.  This will download and install the optional package.  Not all packages
    build properly, but if they don't build they won't be installed.
3.  All the files associated with the installed optional packages will be
    included in the plist file, and so will be deinstalled along with
    everything else when the pkg_delete command is used.
4.  You can also try installing the packages AFTER the port is installed,
    but for some reason this doesn't always work.

AND

5.  Install and use these at your own risk.
