That Parse doesn't parse ("foo.com/path" or "foo.com:443/path") has
become something of a FAQ.

Updates #19779
Updates #21415
Updates #22955

Change-Id: Ib68efddb67f59b1374e8ed94effd4a326988dee7
Reviewed-on: https://go-review.googlesource.com/81436Reviewed-by: Ian Lance Taylor <iant@golang.org>