When we lookup a qualified identifier, we need to unpack
an alias. Do this in all places, not just one. Duh!

Fixes #17716.
For #17592.

Change-Id: I58d57b17cc635d0408b370f109c719c16757fd8e
Reviewed-on: https://go-review.googlesource.com/32534Reviewed-by: Alan Donovan <adonovan@google.com>