path.Join collapses duplicated '/' tokens, but an HTTP URL
intentionally includes a '://' after the scheme.

This should fix the syntax of the errors seen in
https://build.golang.org/log/a17d0c7b6159ea4dad0a9e5378ab5a36ee30ce44.

Updates #52727.

Change-Id: I6e1773a7eb8b3e7e2b3ca29540c1e94a7cd2d99d
Reviewed-on: https://go-review.googlesource.com/c/go/+/461682
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

CL 406675 added more detail to bare errors from net/http in two places.
CL 461682 improved one of the two places to stop folding "//" into "/".
This CL applies the same change to the other place.

For #52727.

Change-Id: I3fc13f30cf0f054949ce78269c52b7fafd477e70
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/go/+/532015
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

CL 233437 added a redactedURL field to proxyRepo, a struct that already
had a field named 'url'. Neither fields were documented, so the similar
names suggest the most natural interpretation that proxyRepo.redactedURL
is equivalent to proxyRepo.url.Redacted() rather than something else.
That's possibly why it was joined with the module version in CL 406675.

It turns out the two URLs differ in more than just redaction: one is the
base proxy URL with (escaped) module path joined, the other is just the
base proxy URL, in redacted form.

Document and rename the fields to make the distinction more clear, and
include all 3 of base module proxy URL + module path + module version
in the reported URL, rather than just the first and third bits as seen
in the errors at https://go.dev/issue/51323#issuecomment-1735812250.

For #51323.
Updates #38680.
Updates #52727.

Change-Id: Ib4b134b548adeec826ee88fe51a2cf580fde0516
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/go/+/532035
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>