Document a risk of generating invalid code due to shadowing between
identifiers in code files and the imported package names.
This risk was present before for any package with more than 1 .go file,
but it's increased when some files have renamed imports (since they're
typically used to resolve shadowing conflicts).
Resolves TODO(adonovan): support renaming imports.
Change-Id: Ie0e702345790fd2059c229623fb99fe645d688a4
Reviewed-on: https://go-review.googlesource.com/23785
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>
