[tz] Clarification on LMT entries

[Paul Eggert]

As I recall, tzdb's circa-1880 transitions in the former Russian empire 
are from Shanks. I have not found independent verification of these 
transitions, and quite possibly they're imaginary. For what it's worth, 
the guess recorded in tzdb lists a transition from local mean time to 
timekeeping based on clocks of major cities nearby, and this guess uses 
KMT to denote "Kiev Mean Time", as noted in the tzdb comment and listed 
in <https://data.iana.org/time-zones/theory.html#abbreviations>. Of 
course we'd like a better source than Shanks for this.

Common practice in 19th-century Russia was to keep Moscow time in train 
stations, regardless of local timekeeping practice. So that is another 
complexity for Kiev.

Another point: these guesses are proleptic, as they use the Gregorian 
calendar and 19-century Russia was firmly in the Julian camp.