. Add a TZUPDATE option, defaulting to on, which will update the time zone
data for the JDK using Sun's tzupdater. 
. Some simplification of the convoluted logic around telling the user
which files to download. In particular, don't care if we've already
told them to download a file.
. Bump PORTREVISION since many North American users will need to pick up
the time zone changes.
Collaboration with: Tim Zingelman <email@example.com>