Use volatile keyword in _PyTime_AsSecondsDouble()

Use volatile keyword in _PyTime_Round()

Filter also values for check_float_rounding().

Filter values which would overflow when converted to a C time_t type.

* Filter values which would overflow on conversion to the C long type
  (for timeval.tv_sec).
* Adjust also the message of OverflowError on PyTime conversions
* test_time: add debug information if a timestamp conversion fails

(About the only new feature that was worth mentioning in
whatsnew without a NEWS entry)

boolean result instead of raising an exception.

Patch by A Kaptur.

boolean result instead of raising an exception.

Patch by A Kaptur.

Drop all hardcoded tests. Instead, reimplement each function in Python, usually
using decimal.Decimal for the rounding mode.

Add much more values to the dataset. Test various timestamp units from
picroseconds to seconds, in integer and float.

Enhance also _PyTime_AsSecondsDouble().

boolean result instead of raising an exception.

Patch by A Kaptur.