tests: change obsolete timestamp to avoid "gmtime()" problem on Windows
Before this patch, "test-obsolete.t" fails on Windows environment,
because strings corresponded to "tm_wday" (day of the week) field are
incorrect.
On POSIX environment, "gmtime()" returns correct "tm_wday" value even
for negative "time_t" value. On the other hand, it returns incorrect
one on Windows environment. At least, "gmtime()" of the Windows
runtime library bundled with Python 2.7.3 does.
According to 9a7d0f7e0561 introducing original timestamp value '56
120', it shouldn't cause negative "time_t" value.
test-obsolete: remove subminute timezone in test
Obsmarker format "1" does not supports sub minute timezone. So we
change the test to something slightly more sensible.
It replaced "-d '56 12'" by "-d '56 120'".