Sync our copy of the timezone library with IANA release tzcode2016j.

Sync our copy of the timezone library with IANA release tzcode2016j.

This is a trivial update (consisting in fact only in the addition of
a comment).  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 1f87181e1 left it.