Sync our copy of the timezone library with IANA release tzcode2017c.

Sync our copy of the timezone library with IANA release tzcode2017c.

This is a trivial update containing only cosmetic changes.  The point
is just to get back to being synced with an official release of tzcode,
rather than some ad-hoc point in their commit history, which is where
commit 47f849a3c left it.