npm / arborist / #876

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Properly handle file:. dep when bundle deps present

If a package had a dependency on `file:.` (ie, to create a symbolic link
to the root project within `node_modules`), as well as a
`bundleDependencies` list, the reifier got into a very strange state and
would fail to resolve its promise, causing npm to exit with a `cb()
never called` error.

The solution is:

- Do not do the extract-and-loadActual pass on dependencies that are
  links.
- Do not create sparse tree folders for dependencies that are links.
  (This wasn't a part of the issue, just a weird inefficiency
  encountered along the way.  We created a dir, only to delete it and
  replace with a symlink later.)
- Later on in the process, when we check to see whether a node has
  already been reified by virtue of having bundleDependencies, instead
  of merely looking at the package.json data, actually keep a list of
  nodes reified ahead of time in this way.
- Lastly, do not run `preinstall`, `install`, and `postinstall` scripts
  for links before linking their bins.  We have to run `prepare` on link
  deps prior to linking their bins, but we should still be linking the
  bins ahead of running the other build scripts, like we do for non-link
  deps.

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