Sync libc/stdtime and zdump(8)/zic(8) with tzcode2008h from elsie.

Sync libc/stdtime and zdump(8)/zic(8) with tzcode2008h from elsie.

There shouldn't be any user visible changes. Some bugs are fixed, among
them an issue with Python's mktime() when TZ wasn't set (reported by
Aran Cox).

Another thing is that this code should behave nicely on architectures with
a 64 bits wide time_t.