go/gcimporter15: support export/import of invalid aliases

+ test

Tested on 1.6, 1.7, and 1.8.

Fixes golang/go#17731.

Change-Id: I06dff4a72ff08ed5e8ae1d23a1e65fe719c03180
Reviewed-on: https://go-review.googlesource.com/32581
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
5 files changed