[tz] tabs in zone.tab

[Zefram]

My automatic repackager for CPAN has just barfed on the zone.tab in
tzdata2012a.  I should have checked the diff more carefully, I guess.
The fault it finds is that the new America/Creston line has *two*
tab characters between "America/Creston" and the region description.
The comments at the top of the file include "Columns are separated by a
single tab.".  Previously the file adhered to the single tab rule, and I
made my parser correspondingly strict.  Obviously I'll manually intervene
to get 2012a repackaged, but I think the file should be fixed for 2012b.

-zefram