Clean up date and timezone handling.
We used to pass changelog dates around as a "unixtime timezone" string
containing a pair of encoded ints. Now, they get passed around as a
(unixtime, timezone) tuple of numbers, which makes much more sense.
unknown
acb14030fe0a tip
acb14030fe0a21b60322c440ad2d20cf7685a376 first
tip 1:b9154636be938d3d431e75a7c906504a079bfe07
first 0:acb14030fe0a21b60322c440ad2d20cf7685a376
b9154636be93 tip
M a
b9154636be93+ tip
acb14030fe0a+ first
acb14030fe0a21b60322c440ad2d20cf7685a376+ first
M a
c8edf04160c7 tip
c8edf04160c7+b9154636be93+ tip
M .hgtags