[PHP-667] Fix off-by-one error deserializing pre-epoch dates

There is no need to subtract one from the "sec" timestamp component if there are no microseconds in the date. Revises: d60995236b254f673a1f24ae3a8fb75e48707e45
Fixed test results and header.

It is required to set a timezone when parsing date/times, as not everybody has
the same zone configured as default.
Merged pull request #273