Using node-mv allows moving files across devices

Using https://github.com/superjoe30/node-mv allows moving files across devices.  node-mv tries `fs.rename` first  then falls back to shell `mv`.  Might be better to use pipes.

These tests fail on my machine even before these changes:

    1) should work with sources as symlinks
    2) should work with sources containing symlinks deeply inside them
    3) should work with sources containing symlinks deeply inside them - with source/**/*
    4) should work with destinations as symlinks