#4 Cf: Automatic synchronization with IERS leap second table

[james woodyatt]

The International Earth Rotation Service (IERS) maintains a web
service that provides the current historical record of leap second
events in the UTC timescale. A table that was current through the
end of 2004 was hardcoded into the Cf_tai64 file.

It would be nice to have an optional service that could synchronize a
host with the IERS bulletin. Such a service would permit Cf_tai64 to
be modified to read a local file periodically to get the leap second
table.