I just saw on the node mailing list that there is a "npm_config_global" env
variable, I could use that.

But the thing about making test-install.sh detect its context is that I'm
not dead sure that will work well on Windows, given its a unix shell
script. Actually, I'm not even sure at the moment that strong-supervisor
installs on Windows, because of the test-install.sh (I'll be testing today
or tomorrow).