Fix http://b/2352067 .

Fix http://b/2352067 .

Time.month ranges over 0..11, not 1..12. Fixed code to deal
properly with this.

Additionally, months with 31 days will crash. Fixed that too.

While we're at it, fix http://b/2354796 (the seconds arc
wasn't synchronized with wall-clock seconds).

Finally, added a bit of additional crash defense in case of
other exceptional situations (e.g. leap seconds, API bugs,
solar flares...)

Change-Id: If42c8fd408cf6619a16541a9661b39e33c5d47a5