Still another try at matching system timezone nicely. On non-Windows

Still another try at matching system timezone nicely.  On non-Windows
machines, break tie scores by preferring shorter zone names over longer;
for names of equal length, prefer the alphabetically first name.  This
yields for example 'EST5EDT' not 'America/New_York' for US eastern time.
On Windows, abandon the whole concept of inspecting the detailed behavior
of the system TZ library, because it doesn't bear inspection :-(.  Instead
use a hardwired mapping table to select our zone name based on the
result of strftime %Z output.  Windows code from Magnus Hagander.