This CL makes sure it matches 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://golang.org/cl/119895
which were not ported to x/tools.
To simplify future comparisons with the original, streamlined
some comments.
Fixesgolang/go#27891.
Change-Id: Iff48c11cb7f0f8a55b4ea33321c686f9d5c707c7
Reviewed-on: https://go-review.googlesource.com/c/142893
Reviewed-by: Alan Donovan <adonovan@google.com>
Robert Griesemer