new ntpleapfetch

[Hal Murray]

The recent ftp=>https change to ntpleapfetch also changed the host from NIST 
to IETF.

-LEAPSRC="ftp://ftp.nist.gov/pub/time/leap-seconds.list"
+LEAPSRC="https://www.ietf.org/timezones/data/leap-seconds.list"

The IETF seems to be a bit slow on updating things.  In particular, they are 
currently one rev behind.

#       Updated through IERS Bulletin C56
#       File expires on:  28 June 2019

#       Updated through IERS Bulletin C55
#       File expires on:  28 December 2018

Should we find a better source or try to work out a way to contact the IETF 
and remind them at the appropriate times?

-- 
These are my opinions.  I hate spam.