I think the test was meant to test requests to 'localhost:80' instead
of 'localhost:80:80'. It passes even with 'localhost:80:80' because
net.SplitHostPort fails inside useProxy. Please comment if you want to
leave old 'localhost:80' is the list too to check old code path.

Change-Id: Ic4cd21901563449e3d4e2f4c8caf723f4ca15bac
u
Reviewed-on: https://go-review.googlesource.com/4293Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>