npm fails on filesystems that don't support symlinks

[anatoly techtonik]

npm fails to install packages. The only reason why it could be is that mounted /vagrant folder doesn't support symlinks. Detailed report:

https://github.com/gratipay/gratipay.com/issues/2971

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: npm 1.3.10~dfsg-1
ProcVersionSignature: Ubuntu 3.13.0-39.66-generic 3.13.11.8
Uname: Linux 3.13.0-39-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.5
Architecture: amd64
Date: Sun Nov 30 14:03:20 2014
PackageArchitecture: all
ProcEnviron:
 TERM=cygwin
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: npm
UpgradeStatus: No upgrade log present (probably fresh install)