[tz] tzcode test suite

[Paul Eggert]

Steve Summit wrote:
> I think later I discovered
> it was because I wasn't actually hitting *any* zoneinfo files,

Bingo. After doing a 'make install', 'make tests' seems to work. People should 
be able to run tests without installing, though; indeed that should be the 
expected and default way to test. I'll take a crack at if it I find the time.

Here's what the output of 'make tests' looks like on my machine:

./testsuite testcases
scripted tests succeeded; trying exhaustive tests (this may take a minute or two)
./testsuite -x -f 1901-12-14 -t 2038-01-19 -i 1753
exhaustive tests: from 1901-12-14 to 2038-01-19 by 1753
testsuite: no or GMT/UTC time zone set, so no nontrivial tz offset tested
try setting TZ or invoking with -s
2450054 tests completed
all tests completed successfully


I'm not sure what that warning about "no nontrivial tz offset tested" means, but 
I hope we can fix the testsuite to set TZ itself if that's what it needs to do.

The tests took 38 seconds on my 6-year-old work desktop, which is a tad slow for 
my taste, but we can move the expensive tests to 'make check-expensive' or 
perhaps speed up the library and/or tester if we can find the time....