When reading along the article, the extra code added in the final
version is not explained. The main function calls flag.Parse(), for
example, which will cause an error, unless the readers looks at the
entirety of final.go to see the import added.

The file shown to the users no longer has the extra flags. The testing
code is now in a patch that gets applied to final.go in order to create
final-test.go. This is the file that will be used to test the code,
matching final.go as much as possible.

Change-Id: I022f5f6c88e107c8ba5623661d74a8d260d05266
Reviewed-on: https://go-review.googlesource.com/11061Reviewed-by: Andrew Gerrand <adg@golang.org>