Be more careful about ComponentId versus UnitId.
Two big ideas:
* @--dependency@ takes a ComponentId, not UnitId.
I used to think it should be a UnitId but it is
now clear that you want to finger the indefinite
unit id, which can be uniquely identified with
a ComponentId
* When hashing for an InstalledPackageId in
new-build, we should produce a ComponentId,
not a UnitId.
While cleaning up the results, for any codepaths which we don't plan on
implementing Backpack (Distribution.Client.Install, I'm looking at you),
just coerce ComponentId into UnitIds as necessary.
Signed-off-by:
Edward Z. Yang <ezyang@cs.stanford.edu>