swift234

Dependencies: Break out member lookups by the name of the member being looked up.

Right now we just have one notion of providing or using a type (as opposed to a
name). It doesn't matter if you're doing lookups, or checking conformance, or
inheriting from a superclass or protocol -- they're all in the same bucket. I'd
like to split these out so that extending a commonly-used type (like, say, Array)
doesn't cause every file in your target to depend on your extension.

This commit doesn't do anything but start tracking which member names are looked
up. For the other things you can do with a type, it's using a dummy empty name.

Swift SVN r30284