Log Message:
Update to 1.18:

1.18   2015-01-05

- There will be a new leap second on June 30, 2015.

1.17   2015-01-04

- No code changes from the 1.16 release.

1.16   2015-01-04 (TRIAL RELEASE)

- Test fix for systems where IVs are 4 bytes long.

1.15   2015-01-03 (TRIAL RELEASE)

- Trying this again ... Experimental fix for adding very large numbers of
  days. Previously, trying to add more than around 2^28 days could cause
  errors if the result ended up in a leap year. This is being released as a
  trial release because I'm not sure how this change will behave on a 32-bit
  Perl. Reported by KMX. RT #97046.