This CL fixes packages ignoring errors regarding files that have
non .go extensions. Packages can be called with just file names
or path which includes files. These aren't checked at all by
packages if they are go files or not, but it fails silently because
of it.
In more detail, go list fails with named files error in STDERR.
However, that is ignored, because go list notoriously abused STDERR
for non-error messages.
Fixesgolang/go#29899
Change-Id: Ie4dc39da0b87200ebd23e6c607396557685e2807
Reviewed-on: https://go-review.googlesource.com/c/tools/+/164663
Reviewed-by: Michael Matloob <matloob@golang.org>
36c10c0a62