Code review comment for lp://staging/~gary/launchpad/sitepackages-ng-1

I have not included the eggs for this branch in the download-cache branch, pending the re-review of my zc.buildout branch (see my last comment on this merge proposal https://code.edge.launchpad.net/~gary/zc.buildout/support-system-python/+merge/8614).

This branch mostly just uses the new zc.buildout branch (and its friends).

This addresses bug 407408, because it specifies that we don't want to use any system-installed eggs. I actually used the new feature of ``bin/buildout -v`` to see what eggs I was using from the system. I was using several, but they were all provided in the download-cache branch so I simply specified that I no longer wanted to use any of them, and it worked fine. In addition to solving bug 407408, this should generally bring more consistency to our setups. (We are still using site-packages because that gives us packages like lxml, even though they are not provided by eggs. If the system ever provides these as eggs, and we want to use them, we should modify the ``allowed-eggs-from-site-packages`` value to let them through.)

This also adds the new include-site-packages-for-buildout feature. It defaults to false right now, which is what we need for bin/buildout to work on semi-broken system Pythons, so buildout.cfg does not have to specify anything. (This is why I was able to remove the include-site-packages settings.)

It also reinstates the ``allow-picked-versions = false`` setting, because I realized if I just matched up the cases of ipython then it would work. This revealed that we had not specified versions for zope.tales and uuid. I fixed that as well.