These comments were originally introduced together with the changes
for alias declarations, and then reverted when we backed out alias
support.

Reintroduce them.

Change-Id: I3ef2c4f4672d6af8a900f5d73df273edf28d1a14
Reviewed-on: https://go-review.googlesource.com/32826Reviewed-by: Matthew Dempsky <mdempsky@google.com>