Resolve pathnames of exposed modules more efficiently.

[jmm]

This is a followup to #1059. After I submitted that, I was working on an async version, which I didn't have ready yet when you pushed your async implementation, @substack. Then I realized that I don't think it's necessary to even do the resolution in browserify, because it looks like module-deps already does it, before anything else needs access to it.

This changeset relies on related changes to module-deps (browserify/module-deps/pull/65).

This may have some rough edges that need to be smoothed out.

• This currently falls down when doing:

b.require('./somefile');

Whereas this works:

b.require('./somefile', {expose: 'whatever'});

In the former case it leads module-deps to mark the file as builtin which causes transforms not to be run on it. I didn't know that, because tests were passing. I didn't discover it until debugging #1074. One solution would be to set a different prop on the object in b.require(), e.g. exposeAs instead of expose, but that seems kind of silly. I haven't had the chance to do it yet, but I think it would be good to take a closer look at how module-deps is handling that scenario and see if there isn't a correction needed there.

• Further changes may be needed to properly support external modules, but I'll need feedback on b.external() role is unclear #1076 for that.