Package linking is a two-step process.
Without parameters, link will create a globally-installed
symbolic link from prefix/package-name to the current folder.
With a parameters, link will create a symlink from the local node_modules
folder to the global symlink.
When creating tarballs for npm publish, the linked packages are
"snapshotted" to their current state by resolving the symbolic links.
handy for installing your own stuff, so that you can work on it and test it
iteratively without having to continually rebuild.
npm.commands.link(cb) # creates global link from the cwd
# (say redis package)
npm.commands.link(redis, cb) # link-install the package
Now, any changes to the redis package will be reflected in
the package in the current working directory