While working on issue 4028, I noticed that Hudson does not make the global and
per-node environment variables available to the SCM checkout operation. This
is unfortunate.

Tom Huybrechts mentioned there may be a cyclical dependency in adding this
feature, when I asked about issue 4028 on the dev mailing list:
http://www.nabble.com/Re%3A-Issue-4028---node-environment-variables-p24556206.html

I've got a potential patch I will be testing soon.