notary/internal/sumweb: copy notecheck/main.go to client.go
notary/internal/sumweb: copy notecheck/main.go to client.go

This will help just a little bit in the next CL,
in which this file is turned into a library.
There are enough changes that git does
not otherwise recognize the copy.

Change-Id: I83d474457b9bcf34c93f1235f806354d194967d1
Reviewed-on: https://go-review.googlesource.com/c/exp/+/172967
Run-TryBot: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Filippo Valsorda <4f40cda291c5f9634e1affd3db44947af61f705c@golang.org>

golang/exp,golang/exp,golang/exp