Option to install node_modules once in a shared directory and copy them ...

...when installing new modules, instead of running npm install each time
We may have a race condition here. In the case of KQuery for instance, if we deploy 2 different versions, this rimraf can screw up the ongoing deployemnt. I know that it's a case that will probably never occur but we don't know how other people use this awesome open source library so we should be  clear somehow (maybe in the readme) that if they customize the nodeInstalldir, they may not be protected by the lock  mecanism anymore.