アップグレードに失敗。zope-2.7.6 plone-2.0.5に戻す前にpython-2.4.3に対応しているzope-2.8.6にチャレンジ。多分、うまくいかないだろう（笑。
ports www/zope28 make install後、www/plone(2.1.2)を流すと、python-2.3.5_1をmakeし始めたのでこだわるなら、buildしかない模様。
追記：
www/ploneは、plone-2.1.2.tar.gzを展開してコピーしてるだけみたいなので、手で展開して、Products以下にコピー。いちおうインストールできたっぽい。
ports www/zope28 make install 時のメッセージ
To create an instance of Zope please run
make instance
You can set the following Variables in /etc/make.conf
ZOPEINSTANCEBASE Directory where Zope instance should go
(default: /usr/local/www/Zope28)
ZOPEINSTANCENAME Default name for a new Zope instance
(default: none)
If you want have multiple Zope you should run
make instance INSTANCENAME=<somename>
The Instancefiles created by make instance will not be remove when the
port is deinstalled. You'll have to delete them yourself.
** ZEO Instances ** (Optional)
** Please refere to http://zope.org/Products/ZEO/ZEOFactSheet
To create a ZEO instance please run
make zeo [INSTANCENAME=<somename>]
**********************************************************************
****** ATTENTION ***** ATTENTION ***** ATTENTION ***** ATTENTION *****
The default installation directory for Zope Products has changed from
/usr/local/www/Zope28/lib/python/Products
to /usr/local/www/Zope28/Products.
You might have to add the following lines to your zope.conf
products /usr/local/www/Zope28/Products
products $INSTANCE/Products
