MFC r265201
MFC r265201

Fix a 2038 bug.

If time_t is 64-bit (i.e. isn't 32-bit) allow any value of year, not
just years less than 2038.

Don't bother fixing the underflow in the case of years before 1903.

MFC after:	1 week
Sponsored by:	DARPA, AFRL

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