This CL updates the importer to match the original code in the std lib
but for the necessary changes to make the code work in x/tools and
with older versions of the std lib.
Notably, it brings over changes from:
https://go-review.googlesource.com/c/152378
Change-Id: Icaa05303a05a226c710b5923d8574f255651fe47
Reviewed-on: https://go-review.googlesource.com/c/152577
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
555fafe5a2