[Packager] Allow imports that are relative to the project root

[negativetwelve]

This is related to #637.

From that issue to quote @JaapRood:
Browserify and webpack both let you use symlinks in the node_modules folder to reference modules. This is mainly useful for preventing ../../../../ requires.

With a symlink setup from the project root setup like:

ln -s src/app node_modules/app

in any file in the project you can:

var  app = require('app');
var somethingElse  = require('app/lib/something-else');

However, the packager can't resolve them: Requiring unknown module "app".

@ide did some investigation and found that support for symlinks was most likely not going to happen for watchman facebook/watchman#105

To get around this in our app, we've been building a library and keeping it at the project root. With this pull request, we can then find these modules and our import statements are:

import MyLib from "my_lib"
import SomethingElse from "my_lib/very/deep/nested/file/something_else"

from anywhere in our project, not just at the root. This is similar to what resolve.root for those familiar with webpack allows.

Thoughts? I know this isn't a solution to the symlinks problem but it helps alleviate the problem for some use cases and allows us to have clean import statements for our core internal modules.

[negativetwelve]

I'm investing the test failures now

[negativetwelve]

So the test failure happens when we rename a package by changing the name attribute in the package.json from aPackage to bPackage but we leave the filename the same (aPackage).

Is this intended behavior?