Is the manifest class-path good enough?

Hi,
More questions from grokking through the code :)
In `def _write_manifest(ctx):` you wrote `# TODO(bazel-team): I don't think this classpath is what you want`.
I tracked it down to this [gerrit review](https://bazel-review.googlesource.com/#/c/2410/) where you said that you wrote this since you
`... assume the classpath is much larger than that, i.e. your dependencies too. I left this here because it mirrors the super simple existing rule, but I am not sure this works for a larger projects with more dependencies.`
Do you still think so?

Start by reading the _write_manifest(ctx) implementation and the referenced Gerrit review at change 2410. Trace how the manifest classpath is assembled for dependencies, then determine whether the existing behavior covers larger projects; done means reaching and documenting a clear correctness decision.

Written by the indexing model from the issue text.