Add special handling for node v0.6.21-pre
Merge pull request #513 from creationix/node_0_6_21_pre

Add special handling for node v0.6.21-pre
v0.14.0
Don't try to copy `npm` itself with `nvm copy-packages`.

Fixes #504.
Properly pass a space-separated list of packages to `npm install`

Fixes #490.
temp