[tz] thread-safe localtime

[Paul Eggert]

Christos Zoulas wrote:
> I wrote the code and I donate it if that matters, but what's more important
> is that the license on those files is the same as the original tz files since
> the differences are minor.

Ah, OK, thanks.  localtime.c is public-domain, but strftime.c and date.c 
are BSD-licensed.  The important changes here are to localtime.c; if you 
donate all your changes to the public domain, we can merge them into 
localtime.c (strftime.c is just the icing on the cake).  So that should 
address the legal concerns, though there still is the technical problem 
of actually doing the merge.