Add `node_resolve` macro

Adds a `node_resolve` macro for gyp scripts to use. This script is basically the result of `require.resolve(moduleName)` - it returns the root dirname of the specified module relative to the current working directory.

I would expect gyp scripts to use it something like:

``` python
  "dependencies": [
    "<!(node_resolve ogg):libogg"
  ]
```

/cc @shtylman