[ticket/13122] Make phpbb_wrapper_gmgetdate_test more reliable

If you're unlucky, calling time() or similar twice in a row will
give you different results. Facebook runs these tests thousands of
times a day, so we occasionally get bogus failures.

PHPBB3-13122
Merge pull request #3011 from fredemmott/ticket/13122

[ticket/13122] Make phpbb_wrapper_gmgetdate_test more reliable

* fredemmott/ticket/13122:
  [ticket/13122] Make phpbb_wrapper_gmgetdate_test more reliable