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.
#!/bin/sh
hg init
echo 123 > a
hg add a
hg commit -m "first" -d "0 0" a
mkdir sub
echo 321 > sub/b
hg add sub/b
hg commit -m "second" -d "0 0" sub/b
cat sub/b
hg co 0
cat sub/b
ls sub
true