[tz] zdump new option -i for easier-to-review output

[Paul Eggert]

Jon Skeet wrote:
> hard (both technically and in terms
> of any IANA process required) would it be to start publishing a zip file of
> the tzvalidate output alongside the code and data files, and include just a
> hash within the main data zip file (e.g. as a new file such as
> tzvalidate-sha256.txt)? While I'm happy to keep doing this separately, it
> would obviously be better if it were integrated into the main process.

Something like this sounds like a good idea. I'd be inclined to use tar.gz 
format (as this format is already used by the distribution) as a container for 
zgrep -i format (whatever that turns out to be) for validation. If we distribute 
that, and while we're at it distribute the zic binary-file output (which others 
have requested), then we can use the same mechanism we're already using for 
checksumming distributions.