[tz] PD notices

[Zefram]

I have some code that repackages the tz database, and along the way it
checks that the subset that it's repackaging is in the public domain.
The check is required because not all of the files are PD (some of
the man pages are BSD licensed), and the license statement on the
automatically-generated package needs to be correct.  The code checks
by looking for the notices that are at the top of most of the files.
I have found that it quite frequently gets broken by small changes in
file formatting, or new files with novel format.  2013e broke it by adding
leap-seconds.list, and 2013f has just broken it again by adding NEWS.

Can we come up with some consistent formatting rules to make the PD
notices machine readable?  It doesn't have to be a single structure for
all file types, just a limited repertoire that code can reliably apply.
Or a separate machine-readable list of files with a single statement
that the listed files are all PD.

-zefram